Monsignor Krzysztof Charamsa, a theologian, had worked at the Congregation of the Doctrine of the Faith, the Vatican's doctrinal arm, since 2003, and taught theology at pontifical universities in Rome, which have also dismissed him.
Vatican sacks gay priest
The Vatican said the dismissal had nothing to do with Charisma's reflections on his personal life, which it said "merit respect".
Charamsa, 43, told Italy's Corriere della Sera newspaper and Polish media that he was gay and had a partner. The Church teaches that homosexuality is not a sin but homosexual activity is, and priests, whether heterosexual or gay, take vows of celibacy.
Charasma followed up his media interviews with a packed news conference with his partner and gay activists at a Rome restaurant. They had planned a demonstration in front of the Vatican but changed the venue several hours before it was due to have started.
The Vatican said the dismissal had nothing to do with Charasma's reflections on his personal life, which it said "merit respect".
But it said his interviews and the planned demonstration was "grave and irresponsible" given their timing on the eve of a synod of bishops who will discuss family issues, including the Church's position on gays.
The Vatican said his actions were aimed at subjecting the synod, which Pope Francis opens on Sunday, to "undue media pressure". He presided at prayer vigil for the synod on Saturday night before tens of thousands of people in St Peter's Square.
At the news conference, Charamsa said he wanted to make "an enormous noise for the good of the Church" and apply "good Christian pressure" on the synod not to forget homosexual believers.
"This decision of mine to come out was a very personal one taken in a Catholic Church that is homophobic and very difficult and harsh (towards gays)," he said.
Francis DeBernardo, executive director of New Ways Ministry, which ministers to Catholic gays, said the Vatican's move was "sadly disappointing."
"It is unfortunate that Church leaders did not see Charamsa's announcement as an opportunity for further dialogue with someone they have known and trusted," DeBarnardo said.
At the news conference, Charamsa suggested that a study be made of how many homosexuals work in the Vatican.
"I ask the pope to be strong and to remember us, homosexuals, lesbians, transsexuals and bisexuals as children of the Church and members of humanity," Charamsa said.
The issue of homosexuality and the Church has dominated the aftermath of the pope's visit to the United States last week.
The Vatican has been embarrassed by a row over the pope's meeting during his U.S. trip with Kim Davis, a Kentucky county clerk who went to jail in September for refusing to honor a U.S. Supreme Court ruling and issue same-sex marriage licences.
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