The Fatimid architecture that developed in the Fatimid Caliphate (909–1167 CE) of North Africa combined elements of eastern and western architecture, drawing on Abbasid architecture, Byzantine, Ancient Egyptian, Coptic architecture and North African traditions; it bridged early Islamic styles and the medieval architecture of the Mamluks of Egypt, introducing many innovations.

The wealth of Fatimid architecture was found in the main cities of Mahdia (921–948), Al-Mansuriya (948–973) and Cairo (973–1169). The heartland of architectural activity and expression during Fatimid rule was at al-Qahira (Cairo), on the eastern side of the Nile, where many of the palaces, mosques and other buildings were built. Large-scale constructions were undertaken during the reigns of al-Mui'zz (r. 953–975) Al-Aziz Billah (r. 975–996) and al-Hakim (r. 996–1021).

The Fatimid caliphs competed with the rulers of the Abbasid and Byzantine empires and indulged in luxurious palace building. Their palaces, their greatest architectural achievements, are known only by written descriptions, however. Several surviving tombs, mosques, gates and walls, mainly in Cairo, retain original elements, although they have been extensively modified or rebuilt in later periods. Notable extant examples of Fatimid architecture include the Great Mosque of Mahdiya, and the Al-Azhar Mosque, Al-Hakim Mosque, Al-Aqmar Mosque, Juyushi Mosque and Lulua Mosque of Cairo.

Although heavily influenced by architecture from Mesopotamia and Byzantium, the Fatimids introduced or developed unique features such as the four-centred keel arch and the squinch, connecting square interior volumes to the dome. Their mosques followed the hypostyle plan, where a central courtyard was surrounded by arcades with their roofs usually supported by keel arches, initially resting on columns with leafy Corinthian order capitals. They typically had features such as portals that protrude from the wall, domes above mihrabs and qiblas, and façade ornamentation with iconographic inscriptions, and stucco decorations. The woodwork of the doors and interiors of the buildings was often finely carved. The Fatimids also made considerable development towards mausoleum building. The mashhad, a shrine that commemorates a descendant of the Islamic prophet Muhammad, was a characteristic type of Fatimid architecture. Three Fatimid-era gates in Cairo, Bab al-Nasr (1087), Bab al-Futuh (1087) and Bab Zuweila (1092), built under the orders of the vizier Badr al-Jamali (r. 1074–1094), have survived. Though they have been altered over the centuries, they have Byzantine architectural features, with little trace of the eastern Islamic tradition.

Many of features and techniques of Fatimid architecture continued to be used in the architecture of their successors, the Ayyubids, and more generally in the architecture of Cairo afterwards. Recently, a "Neo-Fatimid" style has emerged, used in restorations or in modern Shia mosques by the Dawoodi Bohra, which claims continuity from the original Fatimid architecture.

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The Fatimid Caliphate originated in an Ismaili Shia movement launched in Salamiyah, on the western edge of the Syrian Desert, by Abd Allah al-Akbar, a claimed eight generation descendant of the Islamic prophet Muhammad, through Muhammad's daughter Fatimah. In 899 his grandson, to be known as Abd Allah al-Mahdi, became leader of the movement. He fled from his enemies to Sijilmasa in Morocco, under the guise of being a merchant. He was supported by a militant named Abu Abd Allah al-Shi'i, who organized a Berber uprising that overthrew the Tunisian Aghlabid dynasty, and then invited al-Mahdi to assume the position of imam and caliph. The empire grew to include Sicily and to stretch across North Africa from the Atlantic to Libya. The Fatimid caliphs built three capital cities, which they occupied in sequential order: Mahdia (921–948) and al-Mansuriya (948–973) in Ifriqiya and Cairo (973–1169) in Egypt.

Mahdia was a walled city located on a peninsula that projected into the Mediterranean from the coast of what is now Tunisia, then part of Ifriqiya. The Carthaginian port of Zella had once occupied the site. Mahdia was founded in 913 by Abdallah al-Mahdi Billah, the first Fatimid imam-caliph. Al-Mahdi built the Great Mosque of Mahdiya, the earliest Fatimid mosque, in the new city. The other buildings erected nearby at that time have since disappeared, but the monumental access gate and portico in the north of the mosque are preserved from the original structure.

Al-Mansuriya, near Kairouan, Tunisia, was the capital of Fatimid Caliphate during the rules of the Imams al-Mansur bi-Nasr Allah (r. 946–953) and al-Mu'izz li-Din Allah (r. 953–975). Built between 946 and 972, it was a circular walled city holding elaborate palaces surrounded by gardens, artificial pools and water channels.

After the Fatimid conquest of Egypt in 969, the caliph al-Mu'izz moved from the city to the new city of al-Qāhira (Cairo) in 973, but al-Mansuriya continued to serve as the provincial capital. In 1057 it was abandoned and destroyed. Any useful objects or materials were scavenged during the centuries that followed. Today only faint traces remain.

The Fatimid general, Jawhar al-Siqilli, built a new palace city near to the old capital of Fustat upon conquering Egypt in 969, which he at first called al-Mansuriya after the capital in Tunisia. When al-Mu'izz arrived in 973, the name was changed to al-Qāhira (Cairo). The new city incorporated elements of the design of al-Mansuriya, although it was rectangular rather than circular in plan. Both cities had mosques named al-Azhar after Muhammad's daughter, Fatima al-Azhar, and both had gates named Bab al-Futuh and Bab Zuwaila. Both cities had two palaces, for the caliph and for his heir, opposite and facing each other.

Some of the most impressive, large-scale Fatimid mosques and palaces were built in Cairo under during the reigns of al-Mu'izz and his successors, al-Aziz and al-Hakim. The reign of Al-Aziz (r. 975–996) is generally considered to have been the most prosperous. Aided in part by funds generated through his father al-Mu'izz's tax reforms, Al-Aziz is credited with at least 13 major building works during this reign, including palaces, a mosque, a fortress, a belvedere, a bridge and public baths. He was responsible for building and expanding much of the great palace complex in Cairo that had been first established under his father. Among other works, he built the Western Palace and ordered the construction of further additions to the Eastern Palace complex, including the "Great Hall" (al-Iwan al-Kabir) and the "Golden Palace" (Qasr al-Dhahab). He also began construction of a large mosque which was completed after his death by his successor, al-Hakim. Under al-Aziz's rule the ceremonial aspects and rituals involving the Fatimid imam-caliph became more elaborate. In contrast to Abbasid practices in Baghdad, in which the caliph's activities were generally confined to the palace, Fatimid ceremonial practices became increasingly integrated with the surrounding urban environment of Cairo. The imam-caliph often went on processions through the city and visited mosques and shrines, including newly-built monuments sponsored by the ruler or his family.

Al-Aziz's mother, Durzan, widow of al-Mu'izz, was also responsible for ordering the commencement of building projects, mainly in the Qarafa area, ordering construction of the second mosque in Cairo, Jami al-Qarafa Mosque, in 975. Similar to the first mosque, Al-Azhar Mosque, it had some fourteen gates but was later destroyed by fire, leaving only its "green mihrab". Durzan is also credited with ordering construction of the Qarafa Palace, a public bath, cistern, or pool, and a royal garden and hydraulic pump for the Abu'l-Ma'lum fortress. She also ordered a well to be built in the courtyard of Ibn Tulun Mosque in 995, a pavilion overlooking the Nile called Manazil al-'izz, and her own mausoleum in Qarafa.

Fatimid fortunes declined in the mid-11th century, but order was temporarily restored by a line of powerful viziers in the late 11th century. The Armenian vizier Badr al-Jamali was a noted builder, sponsoring numerous state architectural projects and restoration works during his rule from 1074 to 1094, particularly with mosques, restoring minarets in Upper Egypt and building mosques in Lower Egypt. He also rebuilt the walls and gates of Cairo. While large-scale mosques and major public works were rare during this later period, smaller mosques and new commemorative shrines (mashhads) attest to the maintenance of a high standard of craftsmanship in art and architecture.

Fatimid architecture drew together decorative and architectural elements from the east and west, and spanned from the early Islamic period to the Middle Ages, making it difficult to categorize. Art historian Jonathan Bloom states that Fatimid art and architecture must be understood in the context not only of Ifriqiya and Egypt (the central territories they occupied), but in the context of the wider Mediterranean world, including the contemporary cultures of the Umayyad Caliphate of Córdoba and the Byzantine Empire. The architecture that developed as an indigenous form under the Fatimids incorporated elements from Samarra, the seat of the Abbasids, as well as Coptic and Byzantine features. Fatimid architecture bridged early Islamic styles and later medieval Islamic architecture, such as that of the Mamluks. The Fatimids were also unusually tolerant of people with different ethnic origins and religious views, and were adept at exploiting their abilities. Thus many of the works of Fatimid architecture reflect architectural details imported from Northern Syria and Mesopotamia, probably in part due to the fact that they often employed architects from these places to construct their buildings. Fatimid architecture in Egypt drew from earlier Tulunid styles and techniques, and used similar types of material. While also consciously adhering to Abbasid architectural concepts, the architecture is more influenced by Mediterranean cultures and less by Iranian.

According to Ira M. Lapidus, public architecture under the Fatimids was an "extension of the ceremonial aspects of the royal court", and was also intricately made. Most early buildings of the Fatimid period were of brick, although from the 12th century onward stone gradually became the chief building material. While Fatimid architecture followed traditional plans and aesthetics, it differed in architectural details such as the massive portals of some mosques and their elaborate façades. Scholars such as Doğan Kuban describe Fatimid architecture as "inventive more in decoration than in broad architectural concept", although he acknowledges that the Fatimids contributed to a distinct style of mosque. The Fatimids introduced or developed the usage of the four-centred keel arch and the muqarnas squinch, a feature connecting the square to the dome. The muqarnas squinch was a complex innovation. In it a niche was placed between two niche segments, over which there was another niche. It is possible that this design had Iranian inspiration. A similar system was applied to window building.

Fatimid architecture in Cairo also displays certain trends in surface decoration. While Samarran (Abbasid) and Byzantine motifs were major sources of inspiration, Fatimid ornamentation evolved to be less repetitive, more complex, and more specially tailored to suit the surface being decorated. Floral, arabesque, and geometric motifs were the main features. Arabic inscriptions were also carved in a Kufic script which became increasingly ornate, often "floriated" or embellished with floral and vegetal motifs. Carved stucco was already in use during the preceding period of Abbasid domination, as seen in the 9th-century Ibn Tulun Mosque, and it continued to be used in Fatimid Cairo, alongside carving in wood and stone. The remains of Fatimid stucco decoration inside al-Azhar Mosque, for example, show the lingering influence of Abbasid motifs but also display Byzantine and Coptic elements. Arches were often outlined with bands of stucco carved with Kufic inscriptions, a trend which was unique to the Fatimid period. Keel arches, used as structural elements, were also employed as a motif in the shape of decorative niches on walls and façades. These niches were ribbed or fluted with a central radiating motif, an idea which appears to be derived from late antique art and which appeared frequently in Coptic art. This motif continued to be used in the architecture of Cairo during later periods. Window grilles were made of stucco fashioned into geometric or floral motifs and, for the first time, they are inset with glass. The use of marble decoration is also documented, but no examples have been preserved in the surviving buildings from this period. Figural representations, which are frequently found on surviving objects of Fatimid art, were likely also a feature of decoration in the now-vanished Fatimid palaces, though probably not in religious architecture where their presence would have been taboo. It is generally believed that the painted decoration of the muqarnas ceiling of the Norman-built Cappella Palatina (12th century) in Palermo, Sicily, which includes figural images, was adopted from the style and techniques of the Fatimid court.

The palaces of the Fatimid caliphs, their greatest architectural achievements, have been destroyed and are known only from written descriptions and archeological evidence.

Historical sources describe Mahdiya as having multiple Fatimid palaces. From the city's main gate a central avenue led to a public square surrounded by three palaces. The palace on the east side, called the Dar al-'Amma, was used for official purposes. Another to the north was the private palace of Caliph al-Mahdi, and another to the south was for his son, Abu'l-Qasim (later enthroned as al-Qa'im). Unlike most palatial cities of the time, these palaces were located close to the coast, overlooking the sea. One of the palaces had a Great Hall, known as the Iwan al-Kabir ("Great Iwan"). Another reception hall, the Majlis al-Baḥr ("Hall of the Sea" or "Maritime Hall") was built next to the harbour itself to host receptions related to the Fatimid navy. The palaces were all built in high-quality white limestone, which was available locally. Some probable fragments of the palace have been found in the city: some columns and capitals were found re-used in later houses and a large mosaic pavement has been excavated. The mosaic pavement features geometric motifs.

Of the three main palaces, only remains of the southern palace have been found. It measured around 85 by 100 metres (279 by 328 ft) and had round corner towers and semi-round buttresses along its outer walls. Inside, it probably had a large central courtyard, though few remains of this have been uncovered. On the north side of this courtyard was a large reception hall of rectangular shape divided into three naves by two rows of pillars or columns. At the back end of the central nave was a small apse where the throne of the crown prince probably stood. Reception halls or throne halls with a similar layout were found in the older Aghlabid palace at Raqqada and in the later Cordoban Umayyad palatial city of Madinat al-Zahra. According to scholar Felix Arnold, the proportions of this hall correspond to an equilateral triangle, with the throne apse situated at one corner of this triangle. Arnold suggests that the equilateral triangle, which was often employed by Islamic artists and architects, was important because its proportions provided the figure on the throne (at one end of the triangle) with an optimal field of view over the rest of the hall. Similar proportions are found in later throne halls in the western Islamic regions, including those of Madinat al-Zahra, but this is the earliest known application of this design in the region.

In 946 the Fatimids began construction of the new capital named al-Mansuriyya (after its founder, the third Fatimid caliph al-Mansur), at a site called Sabra near Kairouan. Unlike Mahdiya, which was built with more strategic and defensive considerations in mind, al-Mansuriyya was built as a display of power and as a base to generate wealth for the growing Fatimid state. The city had a round layout with the caliph's palace at the center, possibly modeled on the Round City of Baghdad. Only sparse remains of the city have been preserved today, as after its abandonment in the 11th century the site was pillaged for its building materials. It appears to have differed from earlier Fatimid palaces in at least one respect its extensive use of water. One excavated structure featured a vast rectangular courtyard mostly occupied by a large pool. At one end of the courtyard was a suite of rooms and two smaller courtyards whose layout has parallels with both earlier Abbasid palaces (such as Ukhaidir) and the halls of Madinat al-Zahra. Al-Mansur's palace is also described by historical sources as facing a large pool of water, in the center of which was another palace connected to it by a footbridge. This use of water was reminiscent of earlier Aghlabid palaces at nearby Raqqada and of contemporary palaces at Madinat al-Zahra, but not of older Umayyad and Abbasid palaces further east, suggesting that displays of waterworks were evolving into symbols of power in this region and period. A contemporary writer, Qadi al-Nu'man, recounted that Caliph al-Mu'izz ordered the transportation of huge antique columns from Sousse to al-Mansuriyya, to be used in the construction of a new "Great Hall". This story is supported by the on-site discovery of fragments of huge columns with a diameter of over 1 metre.

The heartland of architectural activity and expression during Fatimid rule was Cairo, where many of the palaces, mosques and other buildings were built. The Caliphs competed with their rivals of the Abbasid and Byzantine empires, and were known to indulge in furnishing their palaces with "extraordinary splendor". The sprawling palatial complex at the heart of Fatimid Cairo consisted of two major palaces: the Eastern Palace or Great Palace (al-Qasr al-Kabir) and the smaller Western Palace or Lesser Palace (Qasr al-Saghir al-Gharbi). The two palaces were separated by a main street that ran roughly north-to-south – the present-day al-Mu'izz Street – and at the center between was a large public square, Bayn al-Qasrayn (literally, "Between the Two Palaces"), which was the heart of the city and a site of certain ceremonies. The grand entrance to the Eastern Palace, the Golden Gate (Bab al-Dhahab), stood on one side of this square. The palace complex was accompanied by a mausoleum or cemetery, Turbat al-Za'faraan ("The Saffron Tomb"), where the caliphs were buried, whose site is occupied today by the Khan el-Khalili market. In the 12th century, near the end of the Fatimid period, the head of Husayn was transferred from Ascalon and housed in a shrine (now part of Al-Hussein Mosque) inside the cemetery.

The palaces had gold rafters to support the ceilings and Caliphs typically asked for a golden throne encased with a curtain similar to those of the rulers of the Abbasids and Byzantines. Furniture and ceramics were elegantly adorned with motifs of birds and animals which were said to bring good luck, and depictions of hunters, and musicians and dancers of the court which reflected the exuberance of Fatimid palace life. Figural representations are believed to have been incorporated into the architectural decoration itself, as evidence by some surviving examples of woodwork from the palaces. Fountains were installed in the palaces to cool the atmosphere.

In North Africa, the Fatimids also relied on local Berber commanders to govern the western regions of their empire, such as Ziri ibn Manad, the founder of the Zirid dynasty. Ziri's palace at 'Ashir (near the present town of Kef Lakhdar in Algeria) was built in 934 while he was in the service of Caliph al-Qa'im. It is one of the oldest Islamic-era palaces in the Maghreb to have been discovered and excavated. It was built in stone and has a carefully-designed symmetrical plan which included a large central courtyard and two smaller courtyards in each of the side wings of the palace. Some scholars believe this design imitated the now-lost Fatimid palaces of Mahdia.

Another Fatimid palace has also been documented in Ajdabiya, present-day Libya. Its walls were still mostly standing in the early 19th century and its remains were excavated by archeologists in 1952. The archeologists who studied it suggested that the palace was a kind of base camp for Abu'l-Qasim before he was enthroned as the Caliph al-Qa'im. The palace, known locally as al-Qaṣr al-Muḫaṣṣa, is relatively small, measuring 22 by 33 metres (72 by 108 ft). It was built in white limestone, like the palaces of Mahdiya. It had a rectangular layout with round towers at its corners and a square tower at the middle of its two longer sides. Inside, it has a central square courtyard onto which opens a reception hall consisting of an elongated iwan, about 7.1 metres (23 ft) high, finishing in an apse-like projection at the back. The apse, which still partially stands today, was covered by a semi-dome with squinches.

The plan and decoration of Fatimid mosques reflect Shiite doctrine and that the mosques were often used for royal ceremonial purposes. The characteristic architectural styles of Fatimid mosques include portals that protrude from the wall, domes in front of mihrabs and qibla walls, porches and arcades with keel-shaped arches supported by a series of columns, façade ornamentation with iconographic inscriptions and stucco decorations. The mosques followed the hypostyle plan, where a central courtyard was surrounded by arcades with their roofs usually supported by keel arches, initially resting on columns with Corinthian capitals. The arches held inscription bands, a style that is unique to Fatimid architecture. The later columns often had a bell-shaped capital with the same shape mirrored to form the base. The prayer niche was architecturally more elaborate, with features such as a dome or transept. The Fatimid architects built modified versions of Coptic keel-arched niches with radiating fluted hoods, and later extended the concept to fluted domes. The woodwork of the doors and interiors of the buildings was often finely carved.

Early Fatimid mosques such as the Great Mosque of Mahdiya and the mosque of the Qarafa did not have a minaret. Scholar Jonathan Bloom and others have argued that the early Fatimids rejected such structures because they were seen as unnecessary innovations that were symbolically associated with Abbasid architecture at the time. Later mosques built in Egypt and in Ifriqiya incorporated brick minarets, which were probably part of their original designs. These were derived from early Abbasid forms of minaret. Minarets later evolved to the characteristic mabkhara (incense burner) shape, where a lower rectangular shaft supported an octagon section that was capped by a ribbed helmet. Almost all of Cairo's Fatimid minarets were destroyed by an earthquake in 1303.

Some "floating" mosques were located above shops. For the first time, the façade of the mosque was aligned with the street and was elaborately decorated. The decorations were in wood, stucco and stone, including marble, with geometrical and floral patterns and arabesques with Samarran and Byzantine origins. The decorations were more complex than the earlier Islamic forms and more carefully adapted to structural constraints. The imposing architecture and decoration of Fatimid buildings such as the al-Hakim Mosque provided a backdrop that supported the dual role of the Fatimid caliph as both religious and political leader.

The Great Mosque of Mahdiya was built in Mahdia, Tunisia, in 916 CE (303–304 in the Islamic calendar), on an artificial platform "reclaimed from the sea" as mentioned by the Andalusian geographer Al-Bakri, after the founding of the city in 909 by the first Fatimid imam, Abdullah al-Mahdi Billah. Internally, the Great Mosque had a layout similar to other mosques in the region. A transverse aisle paralleled the qibla wall, with nine aisles at right angles to the transverse. Like other mosques in the region, the orientation of the qibla differs significantly from the "true" great circle route to Mecca. In the 11th century, the original qibla wall was destroyed by sea erosion and had to be rebuilt, reducing the size of the prayer hall. Today, the mosque is one of the most well-preserved Fatimid monuments in the Maghreb, though it had been extensively damaged over time and was in large part reconstructed by archeologists in the 1960s.

Unlike other North African mosques, the Great Mosque did not have minarets, and had a single imposing entrance. The entrance is the first known example of a projecting monumental porch in a mosque, which may have been derived from the architecture of secular buildings. A Fatimid mosque at Ajdabiya in Libya had a similar plan, although it did not have the same monumental entrance. Like the Mahdiya mosque, for the same ideological reasons, the Ajdabiya mosque did not have a minaret.

• Great Mosque of Mahdiya
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  Great Mosque of Mahdiya, Tunisia
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  Front view of the Great Mosque of Mahdiya, with projecting entrance visible
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  Interior courtyard of the mosque
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  Interior of the prayer hall, showing arcaded aisles with grouped columns