Mr. O'Malley, a Democrat, announced his decision after vowing in recent weeks to take a more active role in the state’s gay marriage debate. He was criticized by some for remaining too quiet on this year’s gay-marriage bill, which passed the Senate but ultimately died in the House.
His announcement Friday came one month after the New York legislature passed a gay-marriage bill that was vocally championed by its Gov. Andrew M. Cuomo, a Democrat.
“I would like to think that in New York they learned from our experience here, and we will learn from their experience,” Mr. O'Malley said. “This is an evolution in the progress of our state, to be able to perfect our laws so that they more fully protect the rights of every individual.”
The governor’s support is expected to bolster efforts to make Maryland the seventh state to legalize gay marriage, after Republicans and socially-conservative Democrats narrowly fought off a bill in March.
The bill passed the Senate before dying in the House, after at least two House Democrats withdrew their support and party leaders appeared unable to gain the 71 votes needed for passage. Leaders estimated at the time they had about 68 firm supporters.
“It’s very important to have the governor get behind this, just to lead the charge,” said Delegate Maggie McIntosh, Baltimore Democrat who is openly gay. “But it is going to take all of us working together.”
Mr. O'Malley — who before becoming governor said he favored civil unions and believed marriage was intended for a man and woman — said Friday his views have evolved beyond those initially instilled by his Catholic upbringing.
He said he now considers government-recognized marriage a fundamental right.
Mary Ellen Russell, executive director of the Maryland Catholic Conference, said her organization greeted the governor’s announcement with “great disappointment” and said the group would lobby against such a bill.
“We continue to urge members of the Maryland General Assembly not to allow this issue to be driven by partisan politics, and to give full and fair consideration to the legitimate reasons why our state should maintain its recognition of marriage as the union of one man and one woman,” she said.
Mr. O'Malley emphasized that his bill would protect religious organizations that oppose gay marriage from having to honor or accommodate weddings or provide certain services to gay couples.
New York’s law had a similar religious exemption that proved crucial to its passage. It was a major selling point for Mr. Cuomo, who received credit for gathering heavy Democratic support and rounding up four crucial Republican votes in the state’s Republican-controlled Senate.
The bill passed the Senate, 33 to 29, after passing the heavily Democratic Assembly, 80 to 53.
Seeking to take a similar leadership role to New York’s governor, Mr. O'Malley hinted to attendees at a Democratic conference this month in Utah that he could sponsor a Maryland bill if it had the same religious protections.