The cause of death has not been determined, Aponick told a news conference.
Affable, ruddy-faced, and athletic - on Saturday he threw out the first pitch at a Harrisburg Senators game - Bishop McFadden was installed as bishop of the Harrisburg Diocese in August 2010 after six years as an archdiocesan auxiliary and 29 years as a priest.
"This archdiocese was always close to his heart," said Philadelphia Archbishop Charles J. Chaput, who hailed the bishop's efforts to promote vocations and "advance the mission of Catholic education."
Bishop McFadden was perhaps best known locally as overseer of Catholic schools and an accomplished fund-raiser.
"He was tireless. His energy level was absolutely unbelievable," said Richard McCarron, the archdiocese's former secretary for education. "He took Christ's mandate to go and teach really seriously. He saw Catholic education as the best way to transmit the faith to the younger generation."
A graduate of St. Thomas More High School in West Philadelphia, where he was valedictorian, and St. Joseph's University, he taught and coached basketball at West Catholic High School before entering St. Charles Borromeo Seminary in Wynnewood in 1976, when he was 29.
He graduated summa cum laude from the seminary in 1981, the year he was ordained, and quickly caught the eye of Cardinal John Krol, who appointed him his administrative secretary the following year.
He served in that capacity until 1993, when Cardinal Anthony J. Bevilacqua named him president of Cardinal O'Hara High School in Springfield, Delaware County, where he grew enrollment from 1,500 students to 2,000.
Following his consecration as a bishop in 2004, Cardinal Justin Rigali gave him responsibility for overseeing the archdiocesan school system, which continued to see sharp declines in enrollment during his tenure.
"It was a very difficult time for him," McCarron recalled. "He agonized over every [school] closing. But he also knew we have to pay bills."
A member of the education committee of the U.S. Conference of Catholic Bishops since 2006, he was chair of the committee since 2011.
In 2008, Rigali appointed Bishop McFadden to head the archdiocese's capital campaign, "Heritage of Faith, Vision of Hope," which raised pledges of more than $200 million.
It was while assisting Krol at a confirmation at St. John Fisher parish in Boothwyn that then-Father McFadden had first met Gallagher as an altar boy.
"He asked if I was interested in the priesthood," Gallagher recalled. "He saw something I didn't."
The two remained friends, said Gallagher, who described Bishop McFadden as "working 30-hour days. Whenever the phone rang at 10:30 or 11 p.m., I knew it was Joe."
Lisa Fortunato, youth minister at Seven Sorrows of the Blessed Virgin Mary parish in the Harrisburg diocese, described him Thursday as a "very, very humble, gentle, friendly man."
"He was a very easy man to talk to," Fortunato told the Harrisburg Patriot-News. "He was funny, too. He had a really nice sense of humor. He put the kids at ease."
U.S. Sens. Bob Casey and Pat Toomey both issued statements praising the bishop and offering condolences.
Since the Diocese of Harrisburg, which covers 15 counties, has no auxiliary bishop, a body of clergy known as the college of consulters will elect an interim administrator soon after the funeral. That person will serve until Pope Francis appoints a successor.
A viewing will begin at 7 p.m. Sunday, May 5, at St. Patrick's Cathedral, 212 State St., Harrisburg, and continue for two days. The funeral will begin at 10:30 a.m. Wednesday, May 8, at Holy Name of Jesus parish, 6150 Allentown Blvd., Harrisburg. Burial will be in Holy Cross Cemetery, Swatara Township.
Contact David O'Reilly at 856-779-3841 or firstname.lastname@example.org or @doreillyinq on Twitter.