Canon Mary Glasspool, who made her relationship with partner Becki Sanders public, is the second gay bishop to be elected after Bishop Gene Robinson from New Hampshire in 2003.
She was chosen as the assistant bishop for the diocese of Los Angeles.
Warning against the election of Glasspool, Dr Rowan Williams, the Archbishop of Canterbury said that the decision would bring serious implication.
"The election of Mary Glasspool by the Diocese of Los Angeles as suffragan bishop elect raises very serious questions not just for the Episcopal Church and its place in the Anglican Communion, but for the Communion as a whole," Dr Williams said.
Equally disturbed by the appointment, Kendall Harmon, of the conservative diocese of South Carolina said that the decision was damaging and shows defiance of the Christian way of life.
However, the gay and lesbian supporters lauded the decision and said that the selection of a bishop should not be governed by sexual orientation of the person.
"This is another nail in the coffin of Christian homophobia," said Canon Giles Fraser, one of the founders of the liberal Inclusive Church network.