MacNamara comes from the Irish Mac Conmara, "son of the hound of the sea". The surname arose in Co. Clare, where the family were part of the famous Dal gCais tribal grouping. They were second only to the O'Briens, to whom they were hereditary marshals. From relatively minor beginnings, they grew in power to become rulers of the territory of Clancullen, a territory including a large part of what is now east Clare, where they held sway for almost six centuries. They were divided into two septs, the MacNamara Fionn ("Fair") ruling the west of the territory and the MacNamara Reagh ("dark") ruling the east. In the course of their lordship they built dozens of castles, forts and abbeys, including two of the most famous castles in Ireland, Bunratty Castle and Knappogue Castle, both completely restored and in use as banqueting halls. They also built Quin Abbey. down to the final defeat of Gaelic culture in the seventeenth century. Today, the surname is widespread throughout Ireland, but the largest concentration remains in the area of the original homeland, in counties Clare and Limerick..
Brinsley MacNamara (1890-1963), the novelist and playwright, and the most famous modern bearer of the surname, was in fact John Weldon. He adopted the pseudonym as protection; his most famous work, The Valley of the Squinting Windows, was highly critical of Irish life.
Robert MacNamara was U.S. Secretary of Defense from 1961 to 1968 and President of the World Bank from 1968 to 1981.
James MacNamara (1768-1826) a native of Clare, was an officer in the British navy during the Napoleonic Wars and became an admiral in 1814.
Francis MacNamara (1885-1962) was Air Vice-Marshal of the Australian Flying Corps.