People also attributed to him a gift for knowing the future, and a gift for ministering to those with scruples, obsessions or compulsions.
"When God forgives me my sins, he buries them beneath a large stone. It is desecration to root them up again," he would say in response to such cases.
The priest was known for ascetic practices: sleeping on the floor instead of his bed, placing stones in his walking boots, eating the plainest food, and sleeping for only a few hours a night so that he could pray late into the night and early in the day.
Father Sullivan was born in 1861 on Dublin's Eccles Street, not far from the church where he is buried. He was raised in the Protestant Church of Ireland.
His father, Edward Sullivan, was a successful barrister who became Lord Chancellor of Ireland. His mother, Elizabeth Bailey, was a devout Catholic from a prominent County Cork family.
He attended elite Protestant schools in Ireland before studying law in London. For a time, he stopped going to church. His father passed away when he was 24, providing a great shock to him.
By the early 1890s he appeared to have no clear religious views, but was moved by the Confessions of St. Augustine. He began to sit in on religious instruction classes and read a catechism and Butler's Lives of the Saints.
In 1895 the U.K. government appointed him to a commission to investigate widespread massacres of Armenians in Asia Minor. He taught English in Greece and spent time at Mount Athos, a center of Orthodox Christian monasticism.
He was received into Catholic Church in 1896, at the age of 35. The event was a surprise to his family, and though it drew some criticism from some Protestants, Sullivan's reputation was such that he was supported by both Protestant and Catholic friends.
He entered the Society of Jesus four years later.
Father Sullivan died Feb. 19, 1933, aged 71. His death prompted outpourings of appreciation and affection and his funeral turned into a procession through the streets of Dublin.
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His vault at St. Francis Xavier Church has served as a place of prayer for many people, especially those seeking healing. The monthly Mass said for his canonization regularly draws over 200 people.
He was declared a Servant of God in 1960 under Pope John XXIII and declared Venerable by Pope Francis in November 2014.
A Dublin woman's healing from cancer in 1954 after praying for his intercession was recognized as Father Sullivan's first miracle by the Congregation for the Causes of Saints in 2016.