The organisation announced that the money given by the 48-year-old actor, will be used in their efforts in campaigning for marriage equality in some states, reported Ace Showbiz.
"It is unbelievable to me that people's lives and relationships are literally being voted on in a matter of days. In Maine, Maryland, Minnesota and Washington, voters will go to the polls to decide if gay and lesbian couples - our friends and neighbours - are worthy of the same protections as everyone else.
"But that is 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," Pitt said in a statement on the group's website.
Chad Griffin, president of the organisation, thanked Pitt for the donation.
"We're proud to be working with him as we show that fundamental fairness will win at the ballot box," Griffin said.
This is not the first time Pitt has donated money for the cause. He also supplied USD 100,000 in 2008 to strike down California's Proposition 8, which banned gay marriage.
