Born Thomas Sullivan on June 30, 1891 he grew up in the shadows of St. Michael’s Monastery, West Hoboken, New Jersey. At seventeen he entered the Passionist Preparatory School at St. Mary’s Dunkirk, New York. He professed his vows on February 28, 1910 and received the name John Hyacinth. He was ordained to the priesthood on May 30, 1917 in West Hoboken by Bishop Paul Nussbaum.
Father Sullivan taught classics at the Prep School, St. Mary’s Dunkirk. He was an Assistant Pastor at both St. Joseph’s Baltimore, Maryland and St. Joseph’s, Union City. Later he was pastor in Baltimore. He was the first pastor at St. Gabriel’s Parish, Brighton, Massachusetts. He also served as Superior at the St. Vincent Strambi Retreat, Riverdale, New York. From 1949 his eyesight declined and he served as a confessor for priests and lay people.