Director/screenwriter Dustin Lance Black burst into tears after learning a U.S. appeals court had ruled California's ban on same-sex marriage unconstitutional.
Gay unions were made legal for the first time in the state in 2008 but subsequent legislation outlawed them just six months later.
The controversial ruling was reviewed in a federal appeals court and the Proposition 8 bill was overturned in a landmark decision on Tuesday (07Feb12).
Stars including Kelly Osbourne, Mia Farrow and country singer Chely Wright took to their Twitter.com pages to celebrate the ruling, but Black's celebrations were more low-key.
The Milk writer, who had been campaigning for the change, tells The Hollywood Reporter, "It is not cheers and high fives - it is hugs and a far too long delayed sense of respect. So there are tears.
"It was an overwhelming sense of gratitude and almost reverence for what it means to be an American in this country and to finally be told that you are equally respected and you will be equally protected in this country.
"This means so much to us in California and so much to those across the country who want to be married and feel that is in their future. Tonight and tomorrow morning young people across the country - young Lgbt (lesbian, gay, bisexual and transgender) kids - are going to hear that the government respects them and values them and will protect them. That is a life saving message."
However, Black is adamant he will not stop campaigning until every state in the U.S. allows same-sex marriage.
He adds, "At this point we are celebrating a victory. Tomorrow we will get back to the hard work to make sure that marriage applies to every citizen in this country."