Namdalseid was established as a municipality 1 January, 1838 (see formannskapsdistrikt), but is was merged with Beitstad 1 January, 1846. It was separated from Beitstad (again) 1 January, 1904, and celebrated its centennial in 2004.
Being mainly an agricultural municipality, Namdalseid is struggling 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 are fishing, hunting and nature. Having one of the best small-salmon (grisle) rivers in Nord-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 enjoy a spot of hunting.
Namdalseid also has 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.
The first element Namdals- was added around 1550. It is the genitive case of the old region name Namdalen.