Somewhere over the rainbow, on the other side of the Mardi Gras celebrations, there's probably a massive hangover waiting for many of the weekend's revellers.

Glitter, smiles, pumping dance music and a steady stream of marchers were on display as an estimated half-million people lined Sydney streets to watch the 38th annual Mardi Gras parade.

For many of those dancing down the street the evening's parade is just the beginning of a long weekend of partying.

Tom Spillane didn't make it home until the Monday after last year's event and following his appearance as a gilded pirate Viking with Sydney Queer Irish, he's planning to hit the town.

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"He's got the week off work to recover," Mr Spillane's young sister Katie, who travelled from Ireland for the party, told AAP.

The Dykes on Bikes got the night revved up and soon after the first of the 175 floats made its way along the rainbow route.

Emergency services, Defence, the Liberal, Labor and Greens parties and the City of Sydney Council all had floats in the event, which was also politicised by the appearance of both Malcolm Turnbull and Opposition Leader Bill Shorten.

A section of the crowd heralded the arrival of Mr Turnbull with smartphones thrust into the cool night air, hoping to snare a selfie with the first prime minister to visit Mardi Gras.

The PM disappeared into the thick crowd at Taylor Square moments after arriving.

Mr Shorten, however, became the first leader from one of the two major parties to take part.

He also used the event to again promise action on marriage equality within 100 days of the formation of a Labor government.

All of the arriving floats were greeted with cheers but when the revered 78ers marched, rowdy chants gave way to respectful applause, with many gathered yelling "thank you" to the smiling, colourful first veterans of the Mardi Gras.

The 38th Mardi Gras marks a special moment for those pioneers, who received apologies from the state government and police in the lead-up to the event.

Members of the group were bashed by police when they descended on Darlinghurst in June 1978 to protest against the criminalisation of homosexual acts and discrimination against the gay community.

As the march ended and the focus moved to the after-party, clean-up crews were taking to the streets surrounding the parade, preparing to collect the estimated 230kg of glitter used to give the night some sparkle.