When Stuart Henshall and James Brechney were campaigning for same-sex marriage last year, they didn't anticipate they would end up incorporating No vote materials into their own wedding.

But just a few months later they're busy turning "You can say no" posters into confetti as they prepare to tie the knot on a float in the middle of this weekend's Mardi Gras parade.

"We thought wouldn't it be cool to get married at Mardi Gras for the 40th anniversary," Mr Brechney said.

"So it's been a bit of a rush but no regrets yet, it's been amazing."

Mr Brechney proposed to Mr Henshall among a crowd of thousands just moments after the Yes vote in the same-sex marriage survey was announced.

Keen to step it up even further for their nuptials, they're preparing to say 'I do' on top of a giant wedding cake float as it pulls into Sydney's Taylor Square on Saturday night.

The design for the couple's wedding cake float. ( By: ABC News )

"I always wanted a huge wedding so 200,000 people is just enough," Mr Henshall said.

"The thing with Mardi Gras is the floats don't stop for anybody," Mr Brechney said.

"You've got to keep moving your truck so we've quickly got to swap the rings, say I do, sign the forms, throw a confetti canon and we'll be married right there in the heart of Oxford Street."

The pair will be joined on and around the float by a dancing group of family and friends including Mr Brechney's mother Janice.

Family and friends of the couple practice their dance moves ahead of Mardi Gras. ( By: ABC News )

"I love my son dearly and when he first came out [as] gay, you were really worried how society was going to accept him," she said.

"Gee we're coming so far and I'm just so pleased for them."

Organisers promise biggest show yet

Pop icon Cher arrived in Sydney yesterday ahead of her headline performance at the Mardi Gras afterparty.

The parade's creative director Greg Clarke said there was plenty to look forward to earlier in the evening too.

"It's going to be one amazing parade. There's 195 floats, 12,000 participants and of course everyone this year is celebrating Mardi Gras' 40th anniversary," he said.

"You're going to think about and reflect on some of those wonderful moments over the last 40 years, and you're also going to see some amazing expressions of individuality and of pride in who people are."

Mr Clarke said there would be special recognition of the "78ers", the original group of gay and lesbian marchers who were arrested and bashed by police officers during Sydney's first Mardi Gras.

"The first float was that year, it was a ute with a very small sound system and they played four LGBTQI songs off the truck and that's how the parade was born," he said.

"It wasn't just in 1978 though, they were getting together throughout the '70s, numerous different activist groups, and calling for gay rights.

"We're all indebted to all of those wonderful people."

A special program, I Do: 40 Years of Mardi Gras, will air at 10:00pm on March 6 on ABC TV, and at 7:30pm on March 9 on ABC News Channel.