Walker's ruling is coming from a lawsuit brought by two same sex couples seeking to overturn California's voter approved Proposition 8, which restored the state's ban on same sex marriage.
"Most of the experts believe that the case that the other side put on was so weak that they expect Judge Walker to issue a decision that says that the United States constitution protects gay people too, just like everybody else," said Lorri Jean of the L.A. Gay & Lesbian Center.
Supporters from both sides previously said an appeal was certain if Walker did not rule in their favor. The case would go first to the 9th U.S. Circuit Court of Appeals then the Supreme Court if the high court justices agree to review it.
"That is the scary part," Jean said. "This is the most conservative Supreme Court in 70 years in this country so it's not a slam dunk."
While gay rights advocates know they have an uphill battle, supporters of Prop. 8 said they're prepared to go the distance to keep marriage defined as between a man and a woman.
"We're ready to respond and to defend the votes of 7 million Californians that voted to sustain Proposition 8," said Netz Gomez of Protect Marriage.
Walker presided over a 13-day trial that was the first in federal court to examine if states can prohibit gays from getting married.
Supporters argued the ban was necessary to safeguard the traditional understanding of marriage and to encourage responsible childbearing.
Opponents said that tradition or fears of harm to heterosexual unions were legally insufficient grounds to discriminate against gay couples.
Some in West Hollywood's gay community were anxiously awaiting Wednesday's verdict.
"If my parents can accept me, I think society can too," said one man in West Hollywood.
The Associated Press contributed to this report.