Dennis Sullivan was born on March 17, 1945, in the Bronx, New York, to John and Hanorah (née Hayes) Sullivan. He has two brothers, Jack and Charlie, and one sister, Catherine.[1]
Sullivan was ordained to the priesthood for the Archdiocese of New York at St. Patrick's Cathedral in Manhattan by Cardinal Terence Cooke on May 29, 1971.[3] The archdiocese then sent him to the Dominican Republic to further his study of Spanish.[1] He spent three months there, where he "learned to speak Spanish very fast because nobody spoke English."[1]
After Sullivan returned to New York City in 1971, the archdiocese assigned him as curate at the following parishes in New York City:
Sullivan also served as a member of the Lower East Side Catholic Area Conference, the archdiocesan priests' council, and the archdiocesan review board for sexual abuse cases.[1]
As an auxiliary bishop, Sullivan served as the vicar general for the archdiocese. He celebrated the funeral mass of the writer Reverend Richard Neuhaus in January 2009.[5] Within the United States Conference of Catholic Bishops, Sullivan is a member of the Subcommittee on Asian and Pacific Island Affairs and sat on the Catholic Campaign for Human Development Committee from 2005 to 2008.[2]
In January 2014, Sullivan was criticized after the archdiocese purchased a mansion for approximately $500,000 in Woodbury, New Jersey, from Rowan University to serve as the bishop's residence. The diocese responded that the bishop needed the extra room for meetings and conferences.[8] Sullivan in October 2020 announced that the diocese was filing for Chapter 11 bankruptcy protection. He cited the financial effects of the COVID-19 pandemic and sexual abuse lawsuit settlements as the causes.[9]
In 2023, Sullivan was part of the team appointed by Pope Francis to investigate Bishop Joseph Strickland of the Diocese of Tyler in Texas after Strickland criticized the pope.[10] Francis removed Strickland as bishop of Tyler on November 11, 2023.[11]