The Most Ancient Lives of Saint Patrick is a work compiled by Irish cleric James O'Leary. Saint Patrick was a fifth-century Romano-British Christian missionary and bishop in Ireland. Known as the "Apostle of Ireland", he is the primary patron saint of Ireland. The work is compiled with three main objectives in mind. First goal is to present the life of Saint Patrick, avoiding some irrelevant matter and not concerning with the history of the national church which he founded. Second goal was to show his character and his life as it is written in the most ancient original documents, without the influence of later historians who wrote about him. Final objective was to assemble and publish the original documents grouped together.

James O'Leary (1837-1902) was an Irish Roman Catholic cleric.