The Maryknoll religious order said on Monday that Father Ray Bourgeois had been kicked out of the priesthood and the order by the Vatican's doctrinal department, the Congregation for the Doctrine of the Faith.
"The Vatican and Maryknoll can dismiss me, but they cannot dismiss the issue of gender equality in the Church. The demand for gender equality is rooted in justice and dignity and will not go away," Bourgeois said in a statement.
Bourgeois, who had been a priest for 40 years, was disciplined by the Vatican in 2008 after he participated in the invalid ordination of a woman.
"The exclusion of women from the priesthood is a grave injustice against women, our Church and our loving God who calls both men and women to be priests," he said in his statement.
Last year, Bourgeois was among a group of Roman Catholic activists detained by Italian police after they tried to deliver a petition to the Vatican in favor of a female priesthood.
The Vatican says women cannot be ordained priests because Jesus Christ willingly chose only men as his apostles.
Advocates of a female priesthood reject this position, saying Jesus was merely conforming to the customs of his times.
Erin Saiz Hanna, executive director of the U.S.-based Women's Ordination Conference, said the group was "heartbroken" by Bourgeois' dismissal.
"Perhaps no longer a priest in the eyes of the Vatican or Maryknoll community, Father Roy will remain a prophet in the eyes of the marginalized," said Saiz Hanna, who was detained with Bourgeois during last year's protest at the Vatican.