03/10/2016 9:18 AM AEDT | Updated 03/10/2016 9:55 AM AEDT

Margot Robbie Backs Marriage Equality On Saturday Night Live

The Aussie star has made a high-profile stand for same-sex marriage.

Paul Hackett / Reuters
Australian actress Margot Robbie has used a hosting role on SNL to support same-sex marriage.

Aussie actress Margot Robbie used her first-ever hosting role on US TV show Saturday Night Live to call for Australia to legalise gay marriage.

Robbie, star of films like The Wolf of Wall Street and Suicide Squad, wore a black T-shirt with the slogan "Say 'I Do' Down Under" above a rainbow-coloured map of Australia.

While she didn't address the topic directly in her appearance on SNL, Robbie's high-profile display of support for marriage equality in Australia is sure to raise the international profile of the effort to make same-sex marriage a reality down under.

The issue remains divisive in Australia, with the Turnbull government proposing a $160 million plebiscite to resolve it, while Labor and the Greens want a parliamentary vote.

The phrase featured on Robbie's T-shirt, "Say 'I Do' Down Under", is the key message in a new advocacy campaign that's the brainchild of 28-year-old British actor Joshua Sasse.

Sasse, who's also Kylie Minogue's fiance, has launched the new push that comprises a website, Instagram, and hashtag that is likely to get a big boost from Robbie's appearance on the iconic comedy sketch show.

Going from social media, Sasse's campaign already has a number of other celebrity backers.

Robbie's turn on SNL included a number of sketches, including one that skewered her sex symbol status by having her play a fantasy librarian with a subversive secret.

The show also featured veteran actor Alec Baldwin who was at his comedic best as he parodied Donald Trump in the SNL season opener.

The "30 Rock" actor donned a golden wig and looked almost identical to the polarising GOP nominee as he took it to Kate McKinnon as Hillary Clinton in a mock presidential debate.