A firebrand conservative who became one of Pope Francis' most ardent critics has been excommunicated by the Vatican.

Archbishop Carlo Maria Viganò, who once served as the Vatican's ambassador to the U.S., was found guilty of schism. The Vatican's doctrine office imposed the penalty after a meeting of its members on Thursday, a press statement said Friday.

The office cited Viganò's "refusal to recognize and submit to the Supreme Pontiff, his rejection of communion with the members of the church subject to him and of the legitimacy and magisterial authority of the Second Vatican Council," as its reasoning for the ruling.

The Vatican excommunication means that Viganò is formally outside the church, and cannot celebrate or receive its sacraments, for having committed one of the gravest crimes in canon law: schism. A schism occurs when someone withdraws submission to the pope or from the communion of Catholics who are subject to him.

It is considered particularly dangerous to the faith because it threatens the unity of the church. And in fact, Vigano had created a following of like-minded conservatives and traditionalists over the years as he delved deeper and deeper into conspiracy theories about everything from the coronavirus pandemic, to what he called the "Great Reset" and other fringe ideas.

Viganò, during his time as envoy in Washington, also made headlines during Francis' 2015 visit to the United States, which as nuncio he helped organize. Everything was going fine until Viganò arranged for Kim Davis, a Kentucky clerk at the center of the U.S. gay marriage debate, to be among a small group of people at the Vatican residence to greet Francis.

Davis had risen to prominence for refusing to issue all marriage licenses rather than be compelled to issue licenses to same-sex couples. She became a hero to the conservative right in the U.S., with whom Vigano had increasingly identified during U.S. culture wars over gay marriage and religious liberty issues.

After the visit ended, Davis and her lawyers claimed the encounter with Francis amounted to an affirmation of her cause. The Vatican later turned that claim on its head when it released footage of what it said was the "only" private audience Francis had in Washington: with a small group of people that included a gay couple.

Vigano's deception in inviting Davis to meet the pope appeared to put the two on what would become a collision course that exploded in August 2018.

Viganò, who retired in 2016 at age 75, convulsed the Holy See with accusations of sex abuse in 2018, calling on Francis to resign.

As Francis was wrapping up a tense visit to Ireland, Viganò claimed in an 11-page letter that in 2013 he told the pontiff of the allegations of sex abuse against former Cardinal Theodore McCarrick, the most senior U.S. churchmen. But, he wrote, the pontiff ignored that, and allowed McCarrick to continue to serve the church for another five years publicly. He said the pope should resign and subsequently branded him a "false prophet" and a "servant of Satan."

In the letter, Viganò also made a number of ideological claims and was critical of homosexuals within Church ranks. He did not offer any proof for his statements.

The accusations were explosive and helped create the greatest crisis of Francis' then-young pontificate.

The Vatican rejected the accusation of a cover-up of sexual misconduct and last month summoned Viganò to answer charges of schism and denying the pope's legitimacy.

Viganò, who regarded the accusations "as an honor," said he refused to take part in the disciplinary proceedings because he did not accept the legitimacy of the institutions behind it.

"I do not recognize the authority of the tribunal that claims to judge me, nor of its Prefect, nor of the one who appointed him," he said in a statement issued last week, referring to the head of the doctrinal office, Cardinal Victor Manuel Fernandez, and to Francis.

Viganò restated his rejection of Vatican Council II, calling it "the ideological, theological, moral and liturgical cancer of which the (Francis') 'synod church' is the necessary metastasis."

He had not yet commented on the Vatican's ruling on X, his usual forum. About an hour before the Vatican decree was made public, he announced he would be celebrating a Mass on Friday for those who have been supporting him and asked for donations.

McCarrick, the ex-archbishop of Washington, D.C., was defrocked by Pope Francis in 2019 after an internal Vatican investigation found he sexually molested adults as well as children.