The Church of England has dropped its prohibition on gay clergy becoming bishops.
The announcement, from the Church's House of Bishops, would allow clergy in civil partnerships to become bishops if they promised to be celibate.
Conservative evangelical Anglicans say they will fiercely resist the development in the synod.
The issue has split the church since 2003 amid a row over gay cleric Jeffrey John becoming Bishop of Reading.
Mr John, now Dean of St Albans, was forced to step down from the role after protests from traditionalists.
He was also a candidate for Bishop of Southwark in 2010 but was rejected. Evidence emerged that this was because of his sexual orientation.
Evangelicals have warned they would be willing to bring in bishops from overseas to avoid serving under a gay bishop.
The Church has already agreed to allow people in civil partnerships to become clergy, provided they promised they would remain celibate, and repent for active homosexuality in the past.
Those conditions are now to be extended to clergy becoming bishops.
BBC religious affairs correspondent Robert Pigott said given the tension surrounding the issue of sexuality, the Church's decision to allow men in civil partnerships to become bishops represented a major concession and one with considerable symbolic significance