Hollywood star TR Knight has donated $50,000 (£29,000) to help defeat a proposal to remove the rights of lesbian and gay Californians to get married.
Next month the state will vote on Proposition 8.
Mr Knight, who is best-known for his portrayal of Dr George O’Malley on TV hit show Grey’s Anatomy, came out in October 2006, the first actor to publicly confirm he is gay while appearing on one of America’s top-rated shows.
Hollywood names such as Steven Spielberg, Pete Wentz and Brad Pitt have all donated money to the campaign to defeat Prop 8.
It goes to the voters on election day on November 4th.
A new poll of 670 people commissioned by CBS in San Francisco and published this week found that 47% are going to vote for the ban with 42% likely to vote against.
Polling from 11 days ago showed a five point lead for opponents of the measure.
Pollsters SurveyUSA, said:
“Polling on ballot measures in general is an inexact science, and polling on homosexuality in general is a tricky business. So, not too much should be made of the five points that separates ‘yes’ and ‘no’ today.”
More than 11,000 gay and lesbian couples have exchanged vows in California since the state Supreme Court’s ruling in May that same-sex couples have the right to get married.
Prop 8 seeks to remove that right.
TR Knight’s coming out caused a media scandal when it was revealed that he had been the subject of homophobic taunts from co-star Isaiah Washington.
He called Knight a faggot during an on-set confrontation in October 2006, but at the Golden Globes in January he denied the incident had occurred.
After the ceremony, where the show won best drama, he said to journalists, “No, I did not call TR a faggot. Never happened, never happened.”
GLAAD then demanded that Washington apologise for using the word again when denying he used it in the first place.
The actor then signalled his desire to put the controversy behind him by co-operating with GLAAD.