The seminary and the professor "mutually agreed to end their relationship" effective this past Monday, the East Liberty school said. Mr. Gagnon, 59, was a tenured professor of New Testament and had been on the faculty for 23 years.

"We appreciate the contributions Professor Gagnon has made to our students and the community during his time here and we wish him the best in his future endeavors," a seminary statement said.

Mr. Gagnon, in a Facebook post, said the decision was mutual and that his departure had nothing to do with any "moral turpitude."

And while neither the school nor Mr. Gagnon directly linked his departure to his controversial stance on homosexuality, he acknowledged that stance would narrow his prospects for future academic work.

"It is my desire to be forward-looking to the next stage of my career and ministry in the academic world as I seek a new institution in which to teach, research, and minister," he said. "I think God is calling me to an evangelical institution, if the evangelical world will have me."

He said it's "unlikely, given my stances on sexual ethics and Scripture, that any university religion department or mainline denominational seminary would take me."

The Rev. David Esterline, president of the seminary, declined to elaborate on Mr. Gagnon's departure but said the school remained committed to diverse viewpoints.

"My vision is of a seminary as broad as the church of Jesus Christ," he said, including people of "very different understandings of Christian theology."

He said he's committed to a setting where "individuals would hear each other, understand each other and really listen to each other," even being willing to change their minds. He said he's committed to "a learning environment that is safe, maybe not always comfortable, but ... a safe environment."

Mr. Gagnon earned an undergrad degree from Dartmouth College, a master's from Harvard Divinity School and a doctorate from Princeton Theological Seminary.

His writings include the book, "The Bible and Homosexual Practice" -- published in 2001 at a time when several mainline denominations were deadlocked in debates over the role of gay members. In it, he reviews passages throughout the Bible, parsing Hebrew and Greek terms, to argue that "there is clear, strong and credible evidence that the Bible unequivocally defines same-sex intercourse as sin."

Other scholars have disputed his views, saying such passages do not address same-sex relationships as understood today. Mr. Gagnon has never wavered, however, and was quoted in debates over sexuality both within Presbyterian circles and in other Protestant denominations. He also has regularly published in the conservative Catholic journal First Things.

Over time, his view became more the minority among not only his fellow Presbyterians but in society at large, which tipped in favor of same-sex marriage even before the U.S. Supreme Court did in 2015.

Proponents of gay inclusion greeted the news of Mr. Gagnon's departure with relief.

The Rev. Janet Edwards, a minister in the Pittsburgh Presbytery and longtime advocate for same-sex marriage, said she audited a course he taught in introductory Greek and that, while the work was mostly on grammar and vocabulary, he often brought class discussions around to his views on homosexuality.

"I know that he made Pittsburgh Theological Seminary very difficult for a whole generation of students," she said. "It was simply not healthy to interact with him and take a course with him."

The Rev. Dwain Lee, now a pastor in Louisville, Ky., who took a course from Mr. Gagnon, said he found him "extremely pleasant, kind, generally soft-spoken, and genuinely concerned with the well-being of his students."

Rev. Lee, who is in a same-sex marriage, said Mr. Gagnon never pushed his views in class and seemed "the last kind of person that anyone familiar with his writings would imagine him to be."

But Mr. Gagnon's polemical side "was never more than a mouse-click or two away," Rev. Lee wrote in a blog post. "Everyone sitting in his classroom knew about his writings, which are not merely anti-affirming, they're vehemently, almost rabidly, anti-gay."

Mr. Gagnon retains many supporters. His Facebook post contains a long thread of well wishes from those who share his stances, and even from some opponents.

Mr. Gagnon remains active in Eastminster Presbyterian Church in East Liberty, where he is an elder and regularly teaches classes.

"We're sad that he's no longer at the seminary," said its pastor, the Rev. Paul Roberts. "We don't know any of the particulars, but I think it's a loss to the seminary community."

Mr. Gagnon is "such an avid learner of Greek" and fascinated by the nuances in the biblical language, he said. "He's very humorous when he's teaching. We are looking forward to having him teach with us again."

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