Veteran broadcaster Alan Jones became an unlikely champion of gay rights on Wednesday when he delivered a moving speech in support of legalising same-sex marriage on his breakfast radio show.

What began as one of Jones' trademark attacks on Labor leader Bill Shorten, in which he called the Opposition Leader "bereft of ideas" and unelectable, metamorphosed into a heartfelt endorsement of Labor's intention to introduce a bill to Parliament to legalise same-sex marriage.

"I've said it before, I don't understand the complexity of it ... we're not telling anyone what to believe," Mr Jones said at the tail end of his 2GB breakfast program.