John Joseph Krol was born in Cleveland, Ohio, on October 26, 1910, to Polish immigrant parents. By the time he was 18, John Krol was manager of the meat department of a large chain store. However, when a Lutheran co-worker asked him some challenging questions about his faith, John began to turn his attention to matters of religious faith, and first felt called by God to the priesthood. He enrolled in St. Mary's College, Orchard Lake, MI, and from there entered St. Mary's Seminary, Cleveland. On February 20, 1937, he was ordained to the priesthood by Bishop Joseph Schrembs of Cleveland.

After a year of pastoral work in Cleveland, he was sent to study at the Pontifical Gregorian University in Rome, where he received his J.C.L. - Licentiate in Canon Law - in 1940.

He obtained his Doctorate in Canon Law in 1942 at Pontifical Catholic University, Washington, D.C. He was appointed professor of Canon Law at St. Mary's Seminary, Cleveland, a position he held until December 1943. During the papacy of Pius XII, Monsignor Krol was consecrated Auxiliary Bishop of Cleveland and Titular Bishop of Cadi on September 2, 1953.

Archbishop John Krol was installed in the College of Cardinals at the Consistory in the Vatican on June 26, 1967.

During the years after his appointment as Archbishop of Philadelphia on February 11, 1961, Cardinal Krol was instrumental in developing the spiritual well-being of the elderly, campaigned against abortion, reorganized Catholic schools, enlarged the Catholic Social Services and was an active participant in the Christian-unity movement.

On December 8, 1987, Pope John Paul II accepted the resignation of John Cardinal Krol, who had served the Archdiocese of Philadelphia for exactly twenty-seven years.

Cardinal Krol died on Sunday, March 3, 1996. Following a Mass of Christian Burial on Friday, March 8th, he was buried in the crypt of the Cathedral of Saints Peter and Paul in Philadelphia.