This year, the governor has a powerful means of persuasion: He is leading redistricting, the process by which the state draws new districts for lawmakers. But O'Malley said he would not use that as a threat to strong-arm wavering delegates.
O'Malley tasked his top legislative aide with spearheading the effort to move a same-sex marriage bill in 2012.
Joseph C. Bryce, a well-respected presence in Annapolis, said he would put in "as much time as it takes" to secure passage.
Supporters are hoping to pick up a few middle-of-the-road Republicans to support their effort. Democratic Sen. Robert J. Garagiola made a direct appeal to GOP lawmakers during O'Malley's news conference.
"The party of Lincoln and the tea party talk about life, liberty and happiness," he said. "To me this is an issue where Democrats and Republicans can come together."
Only one Republican lawmaker voted for this year's same-sex marriage bill. Sen. Allan Kittleman stepped down as Senate Republican leader after announcing that he would vote for the bill.
Though governors do not typically roll out new priorities in mid-July, supporters said they need as much time as possible to lay the groundwork for support.
Many were caught off-guard late last year when Senate President Thomas V. Mike Miller reconfigured a key committee with more members who supported gay marriage. Though Miller did not support the bill personally, he allowed it to come to a vote and worked to prevent a filibuster.
Aides to O'Malley say the surprise nature of the bill's passage through the Senate left supporters short of time to pull together an effective coalition to ensure success in the House.
But now there's a group of unions, civil liberties groups and some clergy called Marylanders for Marriage Equality, which plan to tap their networks to built support.
McIntosh said that O'Malley's backing would be a "big plus" for the bill. She said that a small group of like-minded lawmakers began talking shortly after the measure failed in the House this year and determined that "everybody needed to be far more visible."
It was then that lawmakers started pressing O'Malley to put his name on the legislation. One key supporter, Sen. Richard S. Madaleno, says that he asked the governor to sponsor a bill every time they saw each other.
Madaleno's 8-year old daughter, Katie Hodge, sat quietly in the front row drawing pencil sketches of her family in a notebook. She pointed out the picture of the Montgomery County Democrat smiling and another of her "other daddy," Mark Hodge.
Several senators said their comfort with Madaleno's family, who frequently visit the State House, led them to support same-sex marriage.
The news conference felt like a reunion of sorts for a group of progressive lawmakers who rode an emotional rollercoaster though the last session. Del. Luke Clippenger, one of seven openly gay House members, said he could hardly contain his excitement. Adjectives he used included "exuberant," "happy" and "joyful."
Peter C. Fosselman, Maryland's deputy secretary of state, attended with Duane Rollins, his partner of 16 years. Fosselman said that he's known the governor for about six years and speaks to him frequently about legal projections for gay couples.
Fosselman once supported civil unions.
"I was for anything that provided legal protections," he said.
Like O'Malley, he decided only recently that gay marriage was a better approach.
He says he changed his mind after watching other states and concluding that civil unions are discriminatory because they create a separate and unequal system for gay people.
Fosselman waited patiently next to a lectern to speak with O'Malley after the event.
The reason, he said: "I want to shake his hand."