On November 12, 1974, Pilarczyk was appointed Auxiliary Bishop of Cincinnati and Titular Bishop of Hodelm by Pope Paul VI. He received his episcopalconsecration on the following December 20 from Archbishop Joseph Bernardin, with Archbishop Nicholas Elko and Bishop James W. Malone serving as co-consecrators. From 1974 to 1982, he served as director of Archdiocesan Educational Services and chairman of the Archdiocesan Commission on Education. He also served as chairman of the governing board of St. Rita School for the Deaf from 1977 to 1982. He once said, "Education means development, growth. When God creates us, He doesn't quite finish it. He lets us do some of the finishing touches. That's what education is. It's a wonderful gift. The ability to become educated... a wonderful gift which sometimes people overlook or misuse." Within the United States Conference of Catholic Bishops, he became a member of the Committee on Doctrine in 1976 and chairman of the Committee on Education in 1978.
Archbishop of Cincinnati
He was appointed Archbishop of Cincinnati—succeeding Joseph Cardinal Bernardin who had been named Archbishop of Chicago—on October 30, 1982. Archbishop Pilarczyk served as vice president and president of the National Conference of Catholic Bishops. During Pilarczyk's tenure there were cases of sexual abuse which were covered up. In 2003, Pilarczyk pleaded no contest to five misdemeanor counts of failing to report felonies and admitted facts that constituted guilt; the archdiocese was found guilty of failing to report its crimes, and the judge said that church leaders had placed self-preservation ahead of their moral duty to minister to the victims. In October 2008, Bishop Dennis Marion Schnurr of the Roman Catholic Diocese of Duluth, Minnesota, was named by Pope Benedict XVI as Pilarczyk's coadjutorarchbishop. This means Schnurr served as the auxiliary bishop and chief vicar general to Pilarczyk, but unlike other auxiliary bishops that had served, he had the right as coadjutor to immediately succeed him as archbishop when Pilarczyk retired. On August 12, 2009, Pilarczyk officially handed in his resignation on his 75th birthday, as mandated by the Vatican. It was formally accepted by Pope Benedict XVI on December 21, 2009. He was immediately succeeded as Archbishop of Cincinnati by Coadjutor Archbishop Schnurr.
After retirement
Pilarczyk continued to be involved in the Greater Cincinnati community, specifically with the growth of the Archdiocese in multiple counties. He expressed a fondness for preaching and worked to address what he considered misconceptions regarding Catholicism. In January 2006, his book entitled Being Catholic: How We Believe, Practice, And Think was published. Pilarczyk wrote at least 12 books on the Catholic faith. After years of declining health, he died on March 22, 2020. His funeral mass, which was streamed online and closed to public attendance due to the COVID-19 pandemic, was held in St. Peter in Chains Cathedral on March 27, 2020.