(Reuters) - The gay half-sister of Republican presidential candidate Newt Gingrich slammed his position on gay rights on Wednesday and said she will support President Barack Obama, a Democrat, in the 2012 election.

Candace Gingrich-Jones, a gay rights activist, told MSNBC's Rachel Maddow that she and her older half-brother, the former speaker of the House of Representatives, were "mutually respectful" but disagree on gay rights.

"He is definitely on the wrong side of history when it comes to those issues," Gingrich-Jones said.

She said she would "work really, really hard to make sure that President Obama is re-elected next year no matter who the Republican candidate is."

Gingrich's campaign nearly sputtered to a halt last summer, but he has recently soared to the top of the polls in the Republican contest to choose a nominee to face Obama in the 2012 election.

Gingrich is known for his socially conservative views and has said he opposes gay marriage. Gingrich-Jones, a director at the Humans Rights Campaign, a gay advocacy group, said he did not attend her wedding.

A spokesman for Gingrich was not immediately available for comment.

(Reporting by Alexandra Alper; Editing by Vicki Allen)