Tickets start at $250 for the event, which will be atop the James Hotel in New York City in mid-September.
The Free State is one of four where same-sex marriage is on the ballot this year. No state has ever upheld gay nuptials at the ballot box, but polling funded by a gay rights group shows Marylanders are open to the idea.
The state will have an unusually crowded ballot this year -- same-sex marriage is one of four controversial laws that voters will decide in November. Others include expanding gambling, allowing some illegal immigrants to have in-state tuition and the congressional map.
Gov. Martin O'Malley, a Democrat with his eyes on the White House in 2016 will appear. He's focusing his energy on same-sex marriage and the in-state tuition questions. (He's said he's "so sick" of the gambling issue.)