Cellach Tosach mac Donngaile was a king of the Uí Cheinnselaig of South Leinster. He belonged to the Sil Chormaic sept of this branch of the Laigin and specifically to a branch which took over leadership of the Uí Dróna -the baronies of Idrone in modern County Carlow. He was the son of Donngal mac Laidcnén and succeeded his uncle Cairpre mac Laidcnén. He ruled from 793 to 809.