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Blue wildebeest are the dominant inhabitants of the Maasai Mara. Around July of each year, these animals migrate north from the Serengeti plains in search of fresh pasture, and return to the south around October. The Great Migration is one of the most impressive natural events worldwide. It involves some 1,300,000 blue wildebeest, 500000 Thomson's gazelles, 97000 topi, 18000 common elands, and 200000 Grant's zebras.

All members of the "Big Five" – lions, African leopards, African bush elephants, African buffaloes, black and white rhinos – are found all year round.

The Maasai Mara is the only protected area in Kenya with an indigenous black rhino population unaffected by translocations. Due to its size, the Mara can support one of the largest populations in Africa. The population of black rhinos was fairly numerous until 1960, but it was severely depleted by poaching in the 1970s and early 1980s, dropping to a low of 15 individuals. Numbers have been slowly increasing, but the population was still only up to an estimated 23 in 1999. The Mara Conservancy, one of the managing bodies of the reserve, reported 120 black rhinos in 1971 and 18 in 1984. They claimed one black rhino in 2001 when they began management and a stable 25-30 in 2023.

Hippopotamuses and Nile crocodiles are found in large groups in the Mara and Talek rivers. The plains between the Mara River and the Esoit Siria Escarpment are probably the best area for game viewing, in particular regarding lion and cheetah.

Large carnivores are found in the reserve. Lions are the most dominant and are found here in large numbers. Spotted hyenas are another abundant carnivore, and will often compete with lions for food. Leopards are found anywhere in the reserve where there are trees for them to escape to. East African cheetahs are also found in high numbers on the open savanna, hunting gazelle and wildebeest. African wild dogs are quite rare here due to the widespread transmission of diseases like canine distemper and the heavy competition they face with lions, who can often ravage their populations. Their packs also roam and travel far distances throughout the plains, making it hard to track them. Smaller carnivores that don't directly compete with the latter include African wolves, black-backed jackals, African striped weasels, caracals, servals, honey badgers, aardwolves, African wildcats, side-striped jackals, bat-eared foxes, Striped polecats, African civets, genets, several mongoose species, and African clawless otters.

Antelopes can be found, including Grant's gazelles, impalas, duikers and Coke's hartebeests. The plains are also home to the distinctive Masai giraffe. The large roan antelope and the nocturnal bat-eared fox, rarely present elsewhere in Kenya, can be seen within the reserve borders.

The area has been named an Important Bird Area by BirdLife International. More than 500 species of birds have been identified in the park, many of which are migrants, with almost 60 species being raptors. It is an important area for the threatened birds that call this area home for at least part of the year. These include: vultures, marabou storks, secretary birds, hornbills, crowned cranes, ostriches, long-crested eagles, African pygmy-falcons and the lilac-breasted roller, which is the national bird of Kenya. The resident Martial eagle is endangered.

As of 2023, Mara Conservancy manages the Mara Triangle on behalf of the county, while the County Government of Narok manages the Narok Sector. The more visited eastern part of the park, known as the Maasai Mara National Reserve, is managed by the Narok County Council. The Mara Triangle in the western part is managed Mara Conservancy, on behalf of the county, since the early 2000s.

The outer areas were administered by ranches of the Maasai community. The land was then subdivided, though some members received greater benefits than the majority of landowners. This weakened regulatory system threatens sustainable management of the Mara.

The Maasai Mara is a major research centre for the spotted hyena. With two field offices in the Mara, the Michigan State University based Kay E. Holekamp Lab studies the behaviour and physiology of this predator, as well as doing comparison studies between large predators in the Mara Triangle and their counterparts in the eastern part of the Mara.

A flow assessment and trans-boundary river basin management plan between Kenya and Tanzania was completed for the river to sustain the ecosystem and the basic needs of 1 million people who depend on its water.

The Mara Predator Conservation Programme also operates in the Maasai Mara, cataloging and monitoring lion populations throughout the region. Concentrating on the northern conservancies where communities coexist with wildlife, the project aims to identify population trends and responses to changes in land management, human settlements, livestock movements and tourism.

Since October 2012, the Mara-Meru Cheetah Project has worked in the Mara monitoring cheetah population, estimating population status and dynamics, and evaluating the predator impact and human activity on cheetah behavior and survival. The head of the Project, Elena Chelysheva, was working in 2001–2002 as Assistant Researcher at the Kenya Wildlife Service (KWS) Maasai-Mara Cheetah Conservation Project. At that time, she developed original method of cheetah identification based on visual analysis of the unique spot patterns on front limbs (from toes to shoulder) and hind limbs (from toes to the hip), and spots and rings on the tail. Collected over the years, photographic data allows the project team to trace kinship between generations and build Mara cheetah pedigree. The data collected helps to reveal parental relationship between individuals, survival rate of cubs, cheetah lifespan and personal reproductive history.

The resilience of the game park model and the impact of the covid pandemic have also been evaluated so as to include consideration of issues of equality, and environmentalism.

The BBC Television show titled "Big Cat Diary" was filmed in the Maasai Mara. The show followed the lives of the big cats living in the reserve. The show highlighted scenes from the Reserve's Musiara marsh area and the Leopard Gorge, the Fig Tree Ridge areas and the Mara River, separating the Serengeti and the Maasai Mara.

In 2018, the Angama Foundation, a non-profit affiliated with Angama Mara, one of the Mara's luxury safari camps, launched the Greatest Maasai Mara Photographer of the Year competition, showcasing the Mara as a year-round destination and raise funds for conservation initiatives active in the Mara. The competition ran for six years, ending in 2023. The inaugural winner was British photographer Anup Shah. The 2019 winner was Lee-Anne Robertson from South Africa. Paolo Torchio won in 2020, Harry Collins in 2021, Preeti and Prashant Chacko in 2022, and Shravan Rao in 2023.

Between 1989 and 2003, ungulates were monitored in the Maasai Mara on a monthly basis; the survey revealed a decline of giraffes by 75%, of common warthogs by 80%, of hartebeest by 76%, and of impala by 67%, attributed to the increased number of livestock grazing in the park and an increase in poaching.

The rise of local populations in areas neighbouring the reserve has led to the formation of conservation organisations such as the Mara Elephant Project. The project aims to ensure the peaceful and prosperous co-existence of humans alongside wildlife. According to the project, human wildlife conflict is seen as a leading threat to the reserve as the population continues to grow. Tourism has increased exponentially. Less than 10 lodges were in the area in the late 1970s. The end of the moratorium saw facilities increase to 140 in 2008, and nearly 200 in 2016.

The growth in population creates a demand for land and resources leading to unplanned infrastructure growth. The weak cash economy creates a need to further subdivide the outlying ranch areas. These new owners have converted some land away from traditional grazing fields, negatively affecting wildlife migration. A rise in fencing exacerbates the restriction in free movement for migration, and grazing opportunities are diminished.

The Mara Conservancy encourages conservation efforts in the Reserve and has accomplished several of their goals since taking stewardship. According to their website, as of 2022 they have arrested 4,500 poachers, vaccinated 100,000 dogs against rabies and distemper, improved access roads, and provided security for the local community and tourist facilities.

• Olare Orok Conservancy

• Walpole, M.; Karanja, G.G.; Sitati, N.W.; Leader-Williams (2003). Wildlife and People: Conflict and Conservation in Masai Mara, Kenya (PDF) (Report). Wildlife and Development Series. Vol. 14. London: International Institute for Environment and Development. ISBN 978-1-84369-416-8. Archived from the original (PDF) on 18 January 2006.

Wikimedia Commons has media related to Maasai Mara.

Wikivoyage has a travel guide for Maasai Mara National Reserve.

• The Mara Triangle