The diocese of Los Angeles has elected only the second openly gay bishop in the global Anglican Church, an issue that has caused deep division.
Rev Mary Glasspool, from Baltimore, was elected assistant bishop, although she needs a majority of national Episcopal Church heads to back her consecration.
The election of the first openly gay bishop, Gene Robinson of New Hampshire, six years ago created a massive rift.
Traditionalists insist the Bible unequivocally outlaws homosexuality.
But liberals believe the Bible should be reinterpreted in the light of contemporary wisdom.
The row led to the formation of a conservative breakaway Episcopal movement in the US - the Anglican Church in North America.
The head of the worldwide Anglican community, the Archbishop of Canterbury Rowan Williams, has been under pressure to recognise it.
BBC religious affairs correspondent Chris Landau says that for an Anglican Communion already fracturing over the issue of homosexuality, this election is yet more evidence of the church's divisions.
He says that for many in the US, electing openly homosexual bishops is simply a reflection of the diversity long affirmed by that Church and that it would be very surprising if Mary Glasspool's election wasn't approved.
This decision represents an intransigent embrace of a pattern of life Christians throughout history and the world have rejected as against biblical teaching
Rev Kendall Harmon,
South Carolina diocese
Episcopal Church leader, Presiding Bishop Katharine Jefferts Schori, has said she will consecrate any bishop whose election follows the rules.
Rev Glasspool is 55 and has been a canon in the Diocese of Maryland for eight years, Associated Press news agency reports.
It says she has been with her partner, Becki Sander, since 1988.
In a statement after her election, Rev Glasspool said: "Any group of people who have been oppressed because of any one, isolated aspect of their persons yearns for justice and equal rights."
The diocese's Bishop J Jon Bruno acknowledged there were rumours of a "concerted effort not to give consent" to Rev Glasspool's election because of her sexuality.
But he said: "I would remind the Episcopal Church and the House of Bishops they need to be conscientious about respecting the canons of the Church and the baptismal covenant to respect the dignity of every human being."
However, one traditionalist clergyman, Rev Kendall Harmon of South Carolina, told AP: "This decision represents an intransigent embrace of a pattern of life Christians throughout history and the world have rejected as against biblical teaching".
Delegates in Los Angeles have been voting for two assistant bishops - the other is Rev Diane M Jardine Bruce.
Bishops of the US Episcopal Church voted in July to overturn a three-year ban on the appointment of gay bishops.
Anglican leaders had asked the Church to observe the moratorium.