Registrars from Brighton and Hove City council will be on hand at a Gay Wedding Show the day before same-sex civil partnerships become legal.
Brian Jones and Anthony Carter prepare their "wedding" suits
The registrars hope to be among the first in England to conduct a "pink wedding". So far 510 provisional bookings have been made in the city.
The Gay Wedding Show is being held at the Hilton Metropole Hotel on Sunday.
On Monday, couples will be able to officially register their intention to sign up for civil partnerships.
The first "wedding" ceremonies will take place 15 days later on December 21, starting in Brighton at 0800 GMT.
The city is Britain's self-styled "gay capital", with 40,000 homosexual residents.
The council said it has had to expand its register office to cope with demand from gay couples.
Mayor Bob Carden will open the wedding show, with Ben Summerskill, chief executive of gay campaign group Stonewall, giving the opening speech.
The registrars will be offering information and advice to couples who want to register their partnerships.
Senior registrar Debra Reynolds said her team were looking forward to the first ceremonies with great excitement.
"Some of our couples have been in stable relationships for 20,30, even 40 years," she said.
Brighton Town Hall will be the venue for some of the first ceremonies
"This is a new, legally recognised form of relationship giving same-sex couples equal rights to heterosexuals."
Hove couple Anthony Carter and Brian Jones, who have lived together for 33 years, are planning to tie the knot at Brighton Town Hall on 21 December.
"I have heard awful stories, where if one partner is seriously ill the hospital will not given the other any information because they are not next of kin," said Mr Jones.
"That is very, very important.
"And after all this time, we wouldn't still be together if we weren't devoted to each other."
Another couple planning to "marry" on the same day are the Rev Debbie Gaston, 46, and her partner of 16 years Elaine Cook, 53.
Ms Gaston is a priest at Brighton's Metropolitan Community Church and has said the couple have waited many years to be able to make the commitment to each other.