"It was really in June when Rep. McCarter and I, who've been talking about this for a while, took the lay of the land and found our colleagues were ready to support this issue," Sims said. "We've been seeing this growing support, so it's the right time."
The gay-marriage debate really picked up steam after the U.S. Supreme Court struck down the Defense of Marriage Act in June, ruling that the government must provide the same benefits to married gay couples as married heterosexual couples. Following that, several Pennsylvania residents filed federal lawsuits challenging the state's ban on same-sex unions, and Pennsylvania Attorney General Kathleen Kane said she would not defend the state marriage law in court.
Montgomery County Register of Wills D. Bruce Hanes this week also filed an appeal of a state court ruling that stopped him from issuing marriage licenses to same-sex couples.
As for the prospects of passage, Sims, who last year became the first openly gay candidate elected to the state Legislature, said he expects the bill to gain approval eventually, if not immediately.
"Like most pieces of legislation, they get introduced and they get moved around, shuffled around and debated. I expect that to be the case with this bill," he said. "I don't have some pie-in-the-sky idea this is going to sail through the Legislature."
But he added: "This bill is going to become law sooner than later."
Ted Martin, executive director of Equality Pennsylvania, an LGBT-advocacy organization, also described the bill's path as challenging.
"In a state where you can still be fired for being gay, it's going to be challenging. But I say in the same breath that you also never know what's going to happen," Martin said. "Who knows?"
Thirteen states and the District of Columbia allow same-sex marriage, including most states in the mid-Atlantic and Northeast, with Pennsylvania in the minority.
Martin said the proposal is encouraging to the LGBT community, especially those younger than 30.
"I think they're looking at this in a way that gives them much hope," he said.
On Twitter: @ChroniclesofSol