Angelina Jolie and fiance Brad Pitt

Angelina Jolie's fiance Brad Pitt wants gay marriage to be legal in the US and has donated $100,000 to a campaign in support of same sex marriage.

The 'Moneyball' actor - who has previously said he won't wed fiancee Angelina until same-sex marriage is legalized - is backing the Human Rights Campaign (HRC) in their efforts to campaign for marriage equality in Maine, Maryland, Minnesota and Washington State.

In an email to HRC supporters, Brad wrote: ''It's unbelievable to me that people's lives and relationships are literally being voted on in a matter of days.

''But that's the system we have and I'm not going to back down from the fight for loving and committed couples to have the ability to marry.

''If you're like me, you don't want to have to ask yourself on the day after the election, what else could I have done?''

HRC president Chad Griffin said the organisation is ''proud'' to be supported by the Hollywood superstar.

He said: ''[Brad's money] delivers vital resources into these campaigns.

''We're proud to be working with him as we show that fundamental fairness will win at the ballot box.''

Brad - who raises six children with Angelina - recently admitted he can't see himself marrying until gay marriage is legalised.

Asked about his wedding plans, he said: ''I'm still hoping we'll figure out our marriage equality in the States before then.''

© Bang Showbiz