Bishop Daniel J. Feeney became the Diocese of Portland's seventh Bishop in 1955 following Bishop McCarthy's death. Some years earlier in 1946, Daniel Feeney had been appointed by the Vatican to be Auxiliary Bishop of the diocese during Bishop McCarthy's tenure. He was consecrated at the Cathedral of the Immaculate Conception on September 12, 1955, which also was his fifty-second birthday. A Mainer, who grew up in St. Dominic's Parish, Daniel Feeney was the Diocese's first "native son" bishop.

As auxiliary bishop, Bishop Feeney performed many of the diocese's administrative duties due to Bishop McCarthy's lingering illness. After two years in this capacity, Bishop Feeney's title became Apostolic Administrator of the Diocese, and in 1952 his title again changed to become Coadjutor Bishop with the right of succession. In 1955, upon Bishop McCarthy's death, Bishop Feeney became the sole bishop of 132 parishes, 41 chapels, 62 missions and 23 stations. He became the leader of 229 priests and 236,672 lay people.

During Bishop Feeney's tenure the number of rectories, convents and schools grew. Three new social centers, fifteen parish halls, and the Chancery on Ocean Avenue all came into existence.

Bishop Feeney's strongest emphasis was freeing the Diocese of the debt it had incurred through the bond issue, which saved the Church in Maine from what might have been financial disaster. Bishop Feeney, with much cooperation from priests and the people, retired the bonds on schedule, a feat, in 1963. He considered this his greatest tangible accomplishment.

Because of Bishop Feeney's protracted illness, in 1967 Bishop Peter Gerety was named Apostolic Administrator of the Diocese to handle its day-to-day business. It was under his direction that the Vatican II changes were begun at the Cathedral. The splendid furnishings would give way to simpler ones. A temporary altar facing the people came first, followed by major renovations designed to emphasize the unity of priest and people. Eventually, the Cathedral took on a very contemporary appearance. By 1968, plans were well underway for work on the Cathedral for it's 100th anniversary in 1969.

On September 15, 1969, Bishop Feeney died after spending the last several months of his life at Mercy Hospital. Because the Cathedral was still closed for renovation, the bishop's funeral Mass was held at St. Dominic's Church, the parish in which he felt at home and had spent his youth.