Though the pronunciation of this name is very similar to O'Byrne there is no connexion between the two septs (however, in County Kildare O'Beirne is found as a synonym of O'Byrne). O'Beirne belongs almost exclusively to Connacht. One branch, allied to the MacDermots, and the other leading Roscommon families, in the thirteenth century displaced the O'Monahans as chiefs of a territory called Tir Briuin between Elphin and Jamestown on the County Roscommon side of the Shannon, and they appear as such in the "Composition Book of Connacht" (1585); and in 1850 there was still an O'Beirne of Dangan-I-Beirn in that territory. The other branch possessed territory in the adjoining county of Mayo, north of Ballinrobe. At the present time O'Beirnes are chiefly found in Counties Roscomon and Leirim.

While no O'Beirne has left a lasting mark on the history of Ireland several distinguished themselves in the service of France in the eighteenth century. The sept has produced one or two interesting characters who may be mentioned here. Thomas Lewis O'Beirne (1748-1823), though reared a Catholic (his brother was a Parish Priest in County Meath) became a Protestant Bishop of Meath in 1789; and Henry O'Beirne (b. 1851), an Irish emigrant, was well known in America on account of his writings about the Texas Indians, amoung whom he settled permanently.