He was Archbishop of Philadelphia from 1961 to 1988, having previously served as an auxiliary bishop of the Diocese of Cleveland (1953–1961), and was elevated to the cardinalate in 1967 by Pope Paul VI.

[1] Religious questions from a Lutheran co-worker prompted Krol to more deeply study Catholic theology and eventually decide to enter the priesthood.

[5] At St. Mary's, he also operated a small tobacco business, receiving shipments of defective cigars and then selling them to his fellow seminarians.

[3] In his first sermon as archbishop, Krol spoke of the need for civic dedication and virtue, saying, "I am conscious, too, of our beloved country, the bold idealism that inspired it, the courage that gave it birth.

May God grant that our prayers, the moral integrity of our lives, the clarity of our teaching, and the sincerity of our patriotism help increase the spiritual resources without which no nation can survive.

[8] During the Council, he served as one of six permanent undersecretaries, with responsibility for keeping a record of votes and distributing, collecting and tabulating ballots.

[10] He was created Cardinal-Priest of S. Maria della Mercede e Sant'Adriano a Villa Albani by Paul VI on June 26, 1967, during the same consistory that elevated Archbishop Karol Wojtyła of Kraków, Poland.

The Grand Jury stated that Krol knew that some priests under his command were molesting and raping young boys and girls but did nothing to prevent future crimes.

A 2005 grand jury report cited evidence that both Cardinal Krol (Archbishop of Philadelphia 1961–1988) and his successor Cardinal Anthony Bevilacqua (Archbishop of Philadelphia 1988–2003) had allowed dozens of sexually abusive priests to stay in holy orders by transferring them from parish to parish to avoid a scandal.

"[1] The Philadelphia Inquirer recalled how Krol was "[ha]iled by conservatives as a defender of the church's heritage and criticized by liberals as an opponent of change.

"[3] However, despite his conservative views on doctrine and church government, he was more liberal on social principles, such as nuclear disarmament and humanitarian programs.

In 1973, he called the Supreme Court's decisions overturning state laws banning abortion "an unspeakable tragedy for this nation" that "sets in motion developments which are terrifying to contemplate."

While mostly in favor, Krol argued that the amendment should drop the exception for when the mother's life was in danger, so that should abortion be banned under all circumstances.

In 1979, his Congressional testimony backing talks on limiting strategic arms foreshadowed an appeal in a pastoral letter by American bishops for nuclear disarmament in 1983.

He opposed many of the small accommodations or options in church discipline that gained favor after Vatican II, including looser regulations governing marriages between Catholics and non-Catholics, the reception of Communion in the hand, and attending Mass on Saturday evening instead of Sunday.