After a 15-year run as spiritual leader to more than a million Roman Catholics in New Jersey, Newark Archbishop John J. Myers is expected to submit a letter to Pope Francis this week seeking the pontiff's permission to retire.

On Tuesday, Myers turns 75, the mandatory retirement age set by canon law. It remains to be seen how swiftly Francis will move to replace him. Some bishops continue to work a year or more after they reach 75.

"The pope can do what he wants," said Christopher Bellitto, a church historian and professor of history at Kean University. "He can accept immediately, or he can say, 'Thanks for the letter. I'll let you know.'"

Given that Francis had previously appointed a coadjutor bishop for the archdiocese, Bellitto said he suspects the pope will move more quickly than he might have otherwise.

When Francis appointed Bernard Hebda as Myers' co-archbishop in September 2013, it was widely seen as a move to steady the archdiocese after controversy over Myers' handling of sexually abusive priests.

Former coadjutor Archbishop Bernard Hebda, right, during a press conference announcing his appointment to the Archdiocese of Newark in September 2013. Hebda was later reassigned to the Archdiocese of Minneapolis-St. Paul. (File photo)

Two years later, Francis named Hebda interim leader of the Archdiocese of Minneapolis and St. Paul, which had been indicted for what a prosecutor described as a systemic failure to protect children from sex abuse.

At the time, Hebda remained Newark's coadjutor archbishop and presumed successor to Myers. That changed in May of this year, when the pope named Hebda the permanent archbishop in Minneapolis.

Myers' successor has been a question mark since.

Jim Goodness, a spokesman for the Newark Archdiocese, said the Vatican had not offered an indication of when a replacement would be named or who might be under consideration. He said Myers' retirement letter was "in the works."

Until a successor is named, Goodness said, Myers will remain heavily involved in running the archdiocese.

"He's working and still teaching and directing the diocese," the spokesman said, adding that the archbishop recently issued a pastoral letter on the eternal desire to search for meaning in the world and how God shapes the human experience.

Once Myers' retirement is approved, Goodness said, he is expected to move to the Hunterdon County home that has served as his weekend residence since 2002.

The five-bedroom house, on 8.2 acres in Franklin Township, became a source of controversy for Myers in February 2014 when The Star-Ledger reported the archdiocese was spending more than $500,000 to build a three-story, 3,000-square-foot wing on the structure, complete with a small indoor exercise pool, three fireplaces and an elevator.

Goodness said Myers will continue to be engaged in church life once he retires, doing "retreat work" and meeting with priests. Myers, a canon lawyer, also continues to serve on the Vatican's council for legislative texts and as chairman of the board of governors for the Pontifical North American College in Rome.

"He's going to be busy," Goodness said.

Bellitto, the church historian, declined to speculate on Myers' replacement, saying Francis' three-year-old papacy has been one of surprises.

"It's the name we don't know that's interesting, because if you look at names, who knew who Blase Cupich was? And he got Chicago," Bellitto said.

Cupich, appointed to the Chicago Archdiocese in 2014, previously served as bishop of Spokane, Wash. Hebda, too, was not well known when he arrived in Newark, having been plucked from the small Diocese of Gaylord, Mich.

Both Cupich and Hebda are viewed as the type of bishops who project an image of compassionate pastoral outreach and frugality in personal life.

The Rev. Thomas Reese, a Jesuit who serves as a senior analyst with the National Catholic Reporter, said he doesn't expect an immediate announcement by the Vatican.

"Rome shuts down in August, so I would not expect something quickly," Reese said by email. "But since everyone knew this was coming, I think we will get someone before the end of the year. If his replacement is announced on his birthday, it means they knew a change was needed quickly."

Myers, an Illinois native ordained in his home state, was named bishop of Peoria, Ill., in 1990. Pope John Paul II appointed him archbishop of Newark in October 2001, as the region was dealing with the aftermath of the Sept. 11 attacks.

He reflected on the difficult period in his recent pastoral letter, writing that Americans posed basic, elemental questions in the face of terrorism and horror.

"These were days and months of profound sadness and human suffering," Myers wrote. "They were also days and months saturated with an abundance of natural goodness and supernatural grace. In the wake of a sudden and massive experience of terror, there followed a sustained search for answers, meaning, solace beyond our daily existence -- a reaching out to the transcendent, a turning toward faith, a search for God."

Mark Mueller may be reached at mmueller@njadvancemedia.com. Follow him on Twitter @MarkJMueller. Find NJ.com on Facebook.