Bishop Arthur Kennedy was born in Boston, Massachusetts in 1942. Ordinary American elements of culture and tasks shaped parts of his life–he was a boy scout and an altar server; had a paper route for two years, and worked in a drug store. He graduated from the Boston Latin School and rowed stroke on the crew team, receiving an athletic letter. He attended the St. John Seminary College in Boston and received a B.A. in Philosophy in 1963. Then, he was sent to the North American College and the Gregorian University in Rome, where he received an S.T.L. in 1967. He was ordained a priest of the Archdiocese of Boston at St. Peter’s Basilica in December 1966.

On his return to Rome he served in two parishes and began his doctoral studies in Systematic Theology at Boston University, where he received a PhD in 1977. In 1974, Cardinal Medeiros released him to the Archdiocese of St. Paul – Minneapolis. There, he both taught and served in several administrative positions for 28 years–including Chair of the Theology Department and Dean of the Master’s program at St. Paul Seminary. In addition, he served at Assumption Parish in downtown St. Paul, and as Archdiocesan Secretary of the Office of Ecumenism. He was one of a small group of faculty who established the Catholic Studies Program at the University.

In 2002, he was appointed as Executive Director of the Secretariat of Ecumenical and Interreligious Affairs for the United States Conference of Catholic Bishops in Washington, D.C. He engaged in dialogue with many religious leaders through 2006.

Finally, Cardinal O’Malley asked him to return to Boston, and appointed him as Rector of St. John’s Seminary where he remained until 2012. On June 30, 2010, Pope Benedict XVI appointed him as Auxiliary Bishop of the Archdiocese of Boston. He was ordained to the episcopal office on September 14, 2010 at Holy Cross Cathedral. In 2012, the Cardinal appointed him Episcopal Vicar of New Evangelization for the Archdiocese. Pope Francis accepted his letter of resignation on June 30, 2017.

From 2012-2018, he was appointed by the Vatican to participate in the Anglican–Roman Catholic International Commission (ARCIC III). He continues to serve on the International Modern Orthodox-Roman Catholic Dialogue.

On September 23, 2023, he was awarded the Priest-Scholar award from the Catholic Studies Department of the University of St. Thomas.