By legislative action, no less. Without a court telling them they had to do it. That makes Maine the second state to enact same-sex marriage without a judicial order to do so, and the first state to enact same-sex marriage without a judicial order to at least create a parallel licensing system (as the Vermont Supreme Court did back before that state created its civil union system). Also, the first state to legislatively dispose of a prior legislative ban (Me. Rev. Stat. Ann. tit. 19-A § 701 (2009)).
My last law school exam ever starts in 10 minutes. Woo hoo!