The Episcopal Church has become the largest US denomination to bless same-sex relationships.
The policy was overwhelmingly approved in a vote at the church's general convention in Indianapolis, Indiana.
Church officials stressed the new ceremony, which includes prayers and an exchange of vows and rings, was not a same-sex marriage.
The US Episcopal Church - part of the 77 million-member Anglican Communion - has nearly two million worshippers.
On Tuesday nearly 80% of the Episcopal Church's House of Deputies voted to authorise a three-year trial run for a provisional same-sex service.

BBC News - US Episcopal Church approves same-sex blessing service