John Sullivan embraced in his life the two main traditions in Irish history: the unionist, anglo-Irish, Church of Ireland tradition and the Catholic tradition of the majority of the population. He was the son of the Lord Chancellor of Ireland, studied in Trinty College, practiced as a lawyer in the English bar, and was known as 'the best dressed man in Dublin'. In his mid-thirties, John became a Catholic and two years later a Jesuit. Most of the rest of his life was spent as a teacher and spiritual father to boys in Clongowes Wood College in Co Kildare. In this relatively remote setting he became known as a poorly-dressed man of prayer and penance with a gift of healing.
Seventy years after his death people continue to visit and pray at his shrine in Gardiner Street church, Dublin.