He was educated at St Anthony's College, Leuven, and returning to Ireland became a priest at Wexford. In 1641, war broke out in Ireland after a Rebellion of Irish Catholics in October of that year. French, along with several other Catholic clerics and gentry, helped to organise the rebels into a more cohesive political movement, the Confederate Catholics of Ireland in March 1642, with the intention of attaining freedom of religion and legal equality for Catholics and self-government for Ireland. The Confederates established their capital at Kilkenny and with the collapse of Royal authority as a result of Civil War became the de facto government of Ireland between 1642 and 1649.