Ussher was born in Dublin, Ireland into a well-to-do Anglo-Irish family. He was a gifted linguist, entering the newly founded (1591) Trinity College Dublin on January 9, 1594, at the age of only thirteen years old. He graduated in 1600 and received a Master's degree in 1601. In 1602, he was ordained in the Trinity College Chapel as Deacon and Priest by his uncle, the Archbishop of Armagh and Primate of All Ireland.
He went on to become a fellow and Professor of Theology in 1607 and then vice chancellor of Trinity on two occasions in 1614 and 1617. In 1621 he was appointed Bishop of Meath and was elevated to the Archbishopric of Armagh in 1625. This placed him at the head of the (Protestant) Church of Ireland, then as now a highly contentious role on the predominently Catholic island. Like many of his contemporaries, he was strongly anti-Catholic and given to frequent denunciations of Catholics, Jews and other "infidels". For instance, his 1626 "Judgement of the Arch-Bishops and Bishops of Ireland" begins:
Ussher spent the last sixteen years of his life in England. He travelled there in 1640 but was unable to return home as a consequence of the Irish rising (1641), the English Civil War (1642) and Oliver Cromwell's Commonwealth regime. Though courted by Parliament, he sided with the king during the Civil War. He died in 1656 at the age of 75 and was given a state funeral in Westminster Abbey, despite his royalist sympathies.
Although Ussher produced a considerable number of religious works, his most famous was the Annales veteris testamenti, a prima mundi origine deducti ("Annals of the Old Testament, deduced from the first origins of the world"), published in 1650. This work established what has become known as the Ussher-Lightfoot Calendar. It is a work that is still referenced by Young Earth Creationists (who believe that the Earth is approximately 6,000 years old) and has been much ridiculed as a symbol of religious obscurantism. See the related article on the Calendar for a discussion of its claims and methodology.