Pope Paul VI appointed Cummins as an auxiliary bishop of the Diocese of Sacramento and titular bishop of Lambaesis. He received his episcopal consecration on May 16, 1974, from Bishop Alden Bell, with Bishops Floyd Begin and Hugh Donohoe serving as co-consecrators, at the Memorial Auditorium in Sacramento As an auxiliary bishop, Cummins continued to serve as executive director of the California Catholic Conference, a position which he held until 1977. Bishop of Oakland Following the death of Bishop Floyd Begin, Pope Paul VI appointed Cummins as the second bishop of the Diocese of Oakland on May 3, 1977. His installation took place on June 30, 1977. In February 1982, Cummins wrote to Cardinal Joseph Ratzinger, then head of the Congregation for the Doctrine of the Faith, forwarding a request from Stephen Kiesle, a priest in the diocese, to be laicized. Kiesle had been convicted of misdemeanor lewd conduct with a child in 1978 and had been suspended by the diocese from ministry. After a request from the Vatican in 1982 for more documentation, Cummins heard nothing from Ratzinger until 1985, when Cummins was told the matter would take more time. Kiesle was finally defrocked in 1987. Cummins served as chairman of the USCCB Liturgy Committee (1981–84), the Laity Committee (1988–91), and the Migration and Refugee Services Committee (1995–98). From 1992 to 1995, he was co-chair of the Roman Catholic-Reformed-Presbyterian Dialogue Commission and a consultant of the Ecumenical and Religious Committee. Cummins was president of the California Catholic Conference from 1988 to 1997. He was chairman of the Catholic Legal Immigration Network, Inc. (CLINIC) from 1995 to 1999, and served as a delegate to several synods in Rome. Retirement After reaching the mandatory retirement age of 75 for bishops, Cummins resigned as Bishop of Oakland on October 1, 2003. That same day, Saint Mary's College of California in Moraga, California, announced that Cummins would be working in the newly established John S. Cummins Catholic Institute for Thought, Culture and Action. On April 4, 2004, Cummins testified for the plaintiffs in a sexual abuse lawsuit against the Diocese of Oakland. The plaintiffs were two brothers, Bob and Tom Thatcher, who charged that Robert Ponciroli, a priest at St. Ignatius Parish in Antioch, California, molested them when they were minors in the early 1980s. Cummins said that he learned about allegations against Ponciroli in 1995, but did not notify police or try