On the death of
Eochu macDiarmaid, the Bishop of Armagh, in January 598, Senach was appointed as the 14th
coarb in succession to
Saint Patrick. The Annals of the Four Masters for 457 AD state "
Ard Mhacha was founded by Saint Patrick, it having been granted to him by Daire, son of Finnchadh, son of Eoghan, son of Niallan." So Senach’s appointment was probably due to the influence of his family as the original grantors of the land and several Bishops of Armagh came from this same family. Senach reigned as Bishop for 12 years. Thomas Walsh states, without giving the specific source, that "
Senach is mentioned by several annalists as a learned man, and is said to have written valuable tracts on the Scriptures and the works of the Fathers, which are now lost." ==Death==