A marriage equality bill would pass if it was presented in federal parliament this week, Labor leader Bill Shorten says.

Speaking at Melbourne’s annual Midsumma gay pride march on Sunday, Mr Shorten called on the prime minister to go back to being the “old” Malcolm Turnbull who believed in marriage equality.

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Mr Shorten said about 95 per cent of Labor MPs, a sizeable number of Liberal MPs as well as the Greens and non-aligned members of parliament would all vote for gay marriage if they had the option.

Victorian Premier Daniel Andrews took part in the Pride March. Photo: Twitter: Daniel Andrews

As a parade of rainbow-clad men and women filtered in and out of view, Mr Shorten promised that marriage equality could happen under a Labor government without wasting $160 million on a plebiscite.

“Within 100 days we will put legislation in the parliament for marriage equality and all MPs can vote according to their choice,” he promised the crowd.

“Labor will get the job done quickly.”

Mr Shorten said he believed a working majority of Liberal MPs supported gay marriage.

The planned plebiscite was a waste of taxpayers’ money and the issue could be resolved quickly if Mr Turnbull reverted to his “conviction politician” roots, he told reporters.

“People who are very anti-marriage equality are excited for the plebiscite: they don’t want to see a conscience vote in parliament,” he said.

“I’m confident if the new Malcolm Turnbull actually did what the old Malcolm Turnbull said, we could have marriage equality by the end of February in this country.”

Mr Shorten, in a grey suit, was outshone by hundreds of all ages in glittering costumes and feathers, who marched down St Kilda’s Fitzroy Street.

An onlooker told AAP the sound of the bagpipes filtering through the roar of the crowd “roused the spirit”.

“What a lovely day to have a parade,” he said.