Rudd, who considers himself a moderate Christian, won the 2007 election on a platform that supported the former conservative government's legal definition of marriage as a union between a man and a woman.
Rudd said his government's position remained unchanged amid media speculation that he will face a groundswell of support for same-sex marriage at Labor's national conference, due to begin in Sydney on Thursday.
"We are consistent with the policy we took to the last election," he told public broadcaster ABC.
The issue was thrown into the spotlight this week when the Labor Party in Tasmania state voted for the Marriage Act to be amended to allow for same-sex unions.
Rudd stood by his election plank, which banned same-sex marriage but endorsed a national "relationships register" provided it did not "mimic" marriage or undermine existing laws.
"I fully respect the integrity of other same-sex relationships ... but in terms of the policy, it's a matter to which we have been committed for some time," Rudd said.
"I fully accept it's a matter of controversy, and there'll be debate, and there should be. This is an open society where we can debate and discuss these matters."
Rudd said his government had moved rapidly to remove the "other discriminations" in national law against same-sex couples in areas such as pensions, tax and employment.
A recent poll suggested up to 60 percent of Australians supported gay marriage, and the statistics bureau in May announced it would count same-sex couples who declared themselves married in the national census.