An elated US Ambassador to Australia John Berry declared it a proud day to be an American and lauded Australia's leadership on equality after the US Supreme Court ruled same-sex marriage was legal in all 50 states.

The first openly gay US Ambassador to serve in a G20 nation, Mr Berry described what the landmark decision would mean before he spoke at a jazz event performed by the Gay and Lesbian Qwire at the Hellenic Club on Saturday night.

"All of the couples who have been married in the 37 states where it was legal will not feel constrained about where they can live, if they got a job offer in one of those other states, they can move there with comfort noting their marriage will be recognised from state to state, and that their children can be raised and the rights will go with them," he said.

"It's also an important day for us to hold true to our founding values, which is that all people are created equal and they deserve equal protection under the law."

Marriages would not occur in any US Embassy, however.

"Unfortunately the US, unlike the British High Commission, we don't perform marriages in the embassy," he said.

Asked whether he had a message for Australian lawmakers on the issue, Mr Berry said Saturday was a day to celebrate what the US had achieved.

"We recognise the debate here in Australia is one Australia needs to have for itself, we wish you well in that regard," he said.

"For most of my life, I've been involved in the LGBTI [lesbian, gay, bisexual, transgender and intersex] community in the United States for over 25 years. We have looked over the horizon to Australia for our lighthouse of leadership on LGBTI, you've been ahead of us on gays in the military, on employment non-discrimination ... this is the only time where we might be ahead for a little bit.

"We've used Australia as the benchmark for equality in the United States."

Mr Berry praised Justice Anthony M. Kennedy, who wrote the majority judgment, as a "patron saint" of the US LGBTI community.

"He struck down the sodomy laws ... he recently struck down the Defence of Marriage Act, and now today is extending that right throughout all 50 states," he said.

The 5-4 majority decided the US Constitution, through the 14th amendment, guaranteed the right for a same-sex couple to be married.

Mr Berry and his long-time partner Curtis Yee wed in August 2013, a month before he presented his credentials to then governor-general Quentin Bryce.