Namdalseid is a former municipality in Trøndelag county, Norway. The municipality existed from 1838 to 1846 and then again from 1904 until its dissolution in 2020 when it joined Namsos Municipality. It was part of the Namdalen region. The administrative centre of the municipality was the village of Namdalseid. Other villages and farm areas in the municipality included Sjøåsen, Statland, Tøttdalen, and Sverkmoen.

At the time of its dissolution in 2020, the 770-square-kilometre (300 sq mi) municipality was the 144th largest by area out of the 422 municipalities in Norway. Namdalseid was the 348th most populous municipality in Norway with a population of 1,576. The municipality's population density was 2.2 inhabitants per square kilometre (5.7/sq mi) and its population had decreased by 8.4% over the previous decade.

The parish of Namdalseid was established as a municipality on 1 January 1838 (see formannskapsdistrikt law), but it was short-lived. On 1 January 1846, it was merged into the neighboring Beitstad Municipality. On 1 January 1904, the Namdalseid district (population: 1,368) was separated from Beitstad Municipality to form a municipality of its own (once again). During the 1960s, there were many municipal mergers across Norway due to the work of the Schei Committee. On 1 January 1964, the parts of the neighboring Otterøy Municipality that were located south of the Namsenfjorden (population: 571) were transferred to Namdalseid Municipality.

On 1 January 2018, the municipality switched from the old Nord-Trøndelag county to the new Trøndelag county. On 1 January 2020, the neighboring Fosnes Municipality, Namsos Municipality, and Namdalseid Municipality were merged to form a new, larger Namsos Municipality. This occurred because on 16 June 2016, the three municipalities voted to merge as part of a large municipal reform across Norway.

The municipality (originally the parish) is named Namdalseid. This name originally comes from the old Elda farm (Old Norse: Eldueið or commonly shortened to Eið) since the first Eid Stave Church was built there. The first element is eldu which is the name of the local river. The last element is eið which means "path/road between two waters" (here the Beitstadfjorden and Namsenfjorden)". The Vikings used to drag boats across Namdalseid using the rivers and waterways in the area, to get from one fjord to another without having to risk crossing the treacherous Folda fjord by travelling up the sheltered Trondheimsfjord and continuing north along the coast. The passage was much easier in olden times as the sea level was higher and the waterways more numerous, but as recently as 2004 a boatdrag was done to commemorate the old traditions. Nowadays, however, one has to transport the boats by road for a fairly long stretch. Around the year 1550, the prefix Namdals- was added to the name to distinguish it from other places using the common name Eid. The prefix is the genitive case of the old region name Namdalen. Historically, the name of the municipality was spelled Namdalseidet. On 3 November 1917, a royal resolution changed the spelling of the name of the municipality to Namdalseid, removing the definite form ending -et.

The coat of arms was granted on 8 December 1989 and they were in use until 1 January 2020 when the municipality was dissolved. The official blazon is "Per pale trefly-counter-trefly argent and vert" (Norwegian: Kløvd av sølv og grønt ved kløverbladsnitt). This means the arms have a field (background) that is divided vertically by a line that follows a trefoil/clover design that alternates on either side of the line. The background on the left side of the line has a tincture of argent which means it is commonly colored white, but if it is made out of metal, then silver is used. The background on the right side has a tincture of green. The clover leaf shapes and the colors were chosen to symbolize the agriculture, landscapes, and nature within the municipality. Namdalseid was a farming municipality with mainly grass production. The municipal flag has the same design as the coat of arms.

The Church of Norway had two parishes (sokn) within Namdalseid Municipality. It is part of the Nord-Innherad prosti (deanery) in the Diocese of Nidaros.

Churches in Namdalseid

Parish (sokn)	Church name	Location of the church	Year built
Namdalseid	Namdalseid Church	Namdalseid	1858
Statland	Statland Church	Statland	1992

The municipality bordered Flatanger Municipality, Roan Municipality, and Osen Municipality to the west; Namsos Municipality to the north; Åfjord Municipality and Verran Municipality to the southwest; and Steinkjer Municipality to the southeast. Lakes in the region include Gilten and Finnvollvatnet. The river Sverka runs through the western part of the municipality. The Namsenfjorden formed most of the northern border. The highest point in the municipality was the 686-metre (2,251 ft) tall mountain Båeriesvaerie.

While it existed, Namdalseid Municipality was responsible for primary education (through 10th grade), outpatient health services, senior citizen services, welfare and other social services, zoning, economic development, and municipal roads and utilities. The municipality was governed by a municipal council of directly elected representatives. The mayor was indirectly elected by a vote of the municipal council. The municipality was under the jurisdiction of the Namdal District Court and the Frostating Court of Appeal.

The municipal council (Herredsstyre) of Namdalseid was made up of 19 representatives that were elected to four year terms. The tables below show the historical composition of the council by political party.

The mayor (Norwegian: ordfører) of Namdalseid was the political leader of the municipality and the chairperson of the municipal council. Here is a list of people who held this position:

Being mainly an agricultural municipality, Namdalseid struggled with a decline in population, as fewer and fewer people find they can make a living growing crops and raising cattle. Other areas of interest for business were fishing, hunting, and nature. Having one of the best small-salmon (grisle) rivers in Trøndelag, Namdalseid is a haven for fly fishing and attracts many fishermen every year. In addition to fishing many visit Namdalseid to experience the beautiful mountain scenery and to do some hunting.

Namdalseid also had some industry. Hundseth Mølle is one of the largest mills in Norway, Namdal Plast AS is a factory manufacturing fiberglass products, and Pelsberederiet AS is a manufacturer of furs from moose, deer, and other wild animals.

• List of former municipalities of Norway

• Årgårdselva: one of the best salmon rivers in Norway
• Finnvollvatnet Nature Reserve: old growth forest, boreal rainforest, and rich bird life