Cardinal Newman's Apologia Pro Vita Sua is a history of Newman's own path from Anglicanism to the Roman Catholic faith (in which he would become an ordained minister in 1847). Newman had been ordained as a priest of the Church of England in 1825, and many, especially one Charles Kingsley, took offense when Newman left the Church of England. This caused Kingsley to make scathing remarks against Newman. Newman's public defense of himself and his beliefs are contents of this treatise.

The book is divided into five parts which represent periods in Newman's life. The contents demonstrate how Newman goes back and forth in his convictions at several points. He wants to believe in the truth of the Church of England, but eventually resolves on the Roman Catholic faith, as he finds its traditional closer to the original ideas of the early church.

Newman is extremely concerned with theological questions (e.g., the worship of Mary and Monophytism). He is closely attentive to the circumstances of the early church, whose church leaders (such as Augustine of Hippo) he studies a great deal in his decision-making.

Ultimately, the treatise is important both for demonstrating the value of questioning oneself and also as a product of its time; it was written at a time when many were questioning the Church of England, and Anglicanism and Roman Catholicism were under threat from the Whig Party (a Protestant liberal group which Newman feared). The rise of the Whig Party inspired Newman to question his religious position.