Members of the URC's ruling general assembly voted in favour at a meeting in Merseyside, although individual churches will not be forced to comply.
The URC becomes the largest Christian organisation in Britain to offer same-sex weddings in its churches.
The Church, which has about 60,000 members, is a Protestant Church with roots in Presbyterianism.
The assembly, meeting in Southport, voted to allow individual congregations to register churches as venues for same-sex marriage services immediately if they wish.
Church officials think the first weddings under the new powers will be able to take place from the autumn.
The couple hoping to marry in church
The Rev John Proctor, general secretary of the URC, said: "Today the URC has made an important decision - at which some will rejoice and with which others will be uncomfortable."
Churches within the denomination which did not wish to perform same-sex marriage ceremonies would not be compelled to do so, he said.
"This has been a sensitive issue for many in our churches.
"It has been important to take our time over the decision process, and to listen as carefully as we can to one another along the way."
Quakers, Unitarians, and some small denominations have already performed same-sex marriage ceremonies.
The Scottish Episcopal Church's general synod will vote for a final time next summer on allowing same-sex couples to marry in churches, after a large majority voted in favour earlier this year.
The United Reformed Church has voted overwhelmingly to allow same-sex couples to marry in its buildings.