Three gay marriage advocates have recalled a conversation in which Kevin Rudd told them he would ''fix'' the marriage law and that Julia Gillard had previously spoken in support of the change when she was a member of his cabinet.

The conversation took place at a party held by gay marriage lobbyists during the Labor Party national conference last December and it included Mr Rudd, then the minister for foreign affairs, the doctor Kerryn Phelps, her partner Jackie Stricker, and another campaigner, Geoff Thomas.

Kevin Rudd ... talked up his support for gay marriage. Credit:Glenn Hunt

''He [Mr Rudd] absolutely said that if he was prime minister it [gay marriage] would have gone through,'' Ms Stricker told The Sun-Herald. ''We couldn't believe how open and forthright he was.''

Mr Thomas, a Vietnam veteran with a gay son, said Mr Rudd told him: ''I hope you know if I was prime minister this would be law.''