Three same-sex couples are to exchange vows in a joint ceremony in Brighton in December, making it the first city in Britain to perform "gay marriages".
Same-sex couples will say their vows in front of two witnesses
Under the Civil Partnership Act, couples can register from 5 December, with ceremonies taking place after a 15-day waiting period.
It allows them to sign a legal document before a registrar and two witnesses.
Brighton and Hove Register Office has selected the couples to be wed one second after midnight on 21 December.
Civil partnerships afford the same rights, protection and expression of commitment to loved ones as to those who are married.
They will allow couples to benefit from a dead partner's pension, grant next-of-kin rights in hospitals and exempt them from inheritance tax on a partner's home.
Partners will also be able to dissolve the agreement in a form of divorce.
Two of those to be married on 21 December, when the law comes into effect, are Gino Meriano, 41, and Mike Ullett, 44, who run the Surrey-based Pink Weddings planning agency.
Mr Meriano said they were looking forward to their "special moment".
"We never had the time to have a commitment ceremony. I really want to get married and I want it as soon as possible," he said.
Brighton and Hove pioneered the launch of the Pink Wedding Waiting List last July when more than 260 gay and lesbian couples signed up their intention to be wed when the law changed.
It has also held more same-sex commitment ceremonies than any other city in the UK and wants to be the first to register a couple on 5 December and marry them.