The Diocese of Pittsburgh includes 61 parish-groupings (107 churches) in the counties of Allegheny, Beaver, Butler, Greene, Lawrence, and Washington, an area of 3,786 sq mi (9,810 km2).

A chapel was built at the fort, dedicated to the Virgin Mary under the title of "The Assumption of Our Lady of the Beautiful River".

In 1844, O'Connor founded a girls' academy and St. Paul's orphan asylum, a chapel for African Americans, the Pittsburgh Catholic and St. Michael's Seminary.

[12] During this period, Catholic immigrants of many nationalities flooded into Western Pennsylvania to work the mines and steel mills.

[12] Pope Benedict XV named Hugh Charles Boyle of Pittsburgh as the sixth bishop of that diocese in 1921.

[19] In 1948, John Dearden of Pittsburgh was appointed coadjutor bishop of the diocese by Pope Pius XII to assist Boyle.

[22] Following the council's advancements in ecumenism, he believed that an "immediate unity in good works and charity" would arise between Catholics and Protestants.

He also established a due-process system to allow Catholics to appeal any administrative decision they believed was a violation of canon law.

In 2003, Wuerl conducted a successful $2.5 million fundraising campaign to create the Catholic Charities Free Health Care Center.

[30] Wuerl reorganized the diocese in response to demographic changes, the decline of the steel industry, and the church's weak financial position.

The diocese objected to a regulation that would force Catholic hospitals and other such institutions to provide health insurance coverage of contraceptives to their employees.

I also am convinced that our clergy and faithful have what it takes to form deep and lasting relationships within their groupings and to create welcoming communities.

"[36] Pope Francis in 2021 issued the motu proprio Traditionis custodes, an apostolic letter that increased restrictions on the celebration of the Tridentine Mass.

The diocese announced that it would continue the daily celebration of the Tridentine Mass at Most Precious Blood of Jesus Parish in Pittsburgh.

[47] In July 1978, a woman called the Pittsburgh Police to complain that Anthony Cipolla had sexually abused her two sons, ages nine and 12.

Cipolla appealed his suspension to the Supreme Tribunal of the Apostolic Signatura, which in March 1993 ordered Wuerl to return him to ministry.

[50][51] In 1985, John O'Connor from the Diocese of Camden was charged with inappropriately touching a 14-year-old boy in Cape May, New Jersey, during a sleepover.

[52] In September 1987, the diocese received an accusation of sexual abuse against three priests: Richard Zula, Francis Pucci and Robert Wolk.

[30] Wuerl informed all diocesan priests that sexual contact with a minor was not merely a sin, but a crime that would result in permanent removal from the ministry and maybe prison.

The diocese created the Diocesan Review Board in 1989 to offer evaluations and recommendations to the bishop on the handling of all sexual abuse cases.

[62] In August 2018, a man from Southeast Asia accused Hugh Lang, the retired pastor of Saint Therese of Lisieux Parish in Munhall, of sexual abuse.

[66] The six dioceses in August 2018 sued the attorney general in the Pennsylvania Supreme Court, opposing the release of the grand jury report.

In 2018, Zubik confirmed that the diocese would release the list of clergy accused of sex abuse when the grand jury report was made public.

Clergy, church employees, and volunteers were all required to go through sexual abuse training programs and criminal background checks.

[70] The report stated that some priests in the diocese ran a child porn ring in the 1970s and 1980s, saying they "used whips, violence and sadism in raping their victims.

[73] In January 2020, a lawsuit against the Diocese of Pittsburgh which was filed by sex abuse survivors, as well as their parents, in September 2018 was allowed to move forward.

[74] In February 2020, it was reported that the lawsuit did not involve requests for monetary awards, but rather greater disclosure of sex abuse records.

[75] On April 15, 2020, a man filed a lawsuit against the Diocese of Pittsburgh for allegedly shielding priests who sexually abused him as a boy.

[76] On August 7, 2020, a new lawsuit was filed against the Diocese of Pittsburgh from a man alleging that Leo Burchianti attacked and raped him twice when he was an altar boy.

[77] Burchianti, who died in 2013, is also accused of having inappropriate sexual relationships with at least eight boys and was previously mentioned in the state grand report.