Visiting singer-songwriter Rufus Wainwright says he was surprised to find Australia hasn't legalised same-sex marriage.

Wainwright says he's enjoying being married, having just tied the knot with theatre producer Jorn Weisbrodt.

"Isn't Sydney the gayest city on earth?" he asked music website Noise11.com.

"I was quite surprised when I got here, I didn't know the deal here, that there was no gay marriage."

Wainwright said he's pleased the US has moved towards allowing legal same-sex marriage in many states, including his native New York.

"Certainly (President Barack) Obama having acquiesced and changed his mind and convinced of the right way - in my opinion - it's a big deal."