A member of the De La Salle Christian Brothers, Gros had served as a high school history teacher, university professor, associate director of the Secretariat for Ecumenical and Interreligious Affairs at the United States Conference of Catholic Bishops; director of Faith and Order for the National Council of Churches; and president of the Society for Pentecostal Studies.
He was awarded a Doctorate in Theology from Fordham University, New York City, in 1973, for his dissertation "Transcendence and Community in Contemporary Social Theory: P. Berger and R. Bellah" under the direction of Wayne Proudfood.
In 1981, Gros was hired as the Executive Director of the Faith and Order Commission of the National Council of Churches (NCC), then headquartered in the Bronx.
He held this post, with responsibilities for ecumenical relations with the western churches and ecclesial communities (Anglican, Mainline Protestant, Evangelical, Pentecostal) until 2005.
He served at the same time as an adjunct professor at the Catholic Theological Union in Chicago, and as President of the Society for Pentecostal Studies.
He was deeply committed to the reception of ecumenical dialogues into religious education and pastoral practice, and worked tirelessly in developing and supporting new generations of ecumenists.
His last was probably "Appreciating the Past and Looking to the Future" which he sent to Koinonia, the Newsletter of the Office of Ecumenism and Interreligious Dialogue published by the Paulist Fathers, just ten days before he died in August 2013.