Barry then turned to non-fiction and published a series of books on religion. These included biographies on religious figures such as Cardinal Newman and Ernest Renan, and on Catholicism in general, with his most notable works being The Papal Monarchy (1902) and Heralds of Revolt (1904). His writings about the medieval papacy were censored by his superiors. Barry also wrote a number of articles for the Catholic Encyclopedia."Barry, Very Reverend Canon William Francis", The Catholic Encyclopedia and Its Makers, Encyclopedia Press, Incorporated, 1917, p. 10 In 1923, he was created a Notary Apostolic by Pope Pius XI. Barry wrote his autobiography, Memories and Opinions (1926), three years later.
