Guerriero entered national politics when he served as president of the Liberty Education Forum and Log Cabin Republicans from January 1, 2003 to September 1, 2006 leading both organizations through periods of unprecedented growth. From 1993-2001, Guerriero won five consecutive elections. He served three terms as a Massachusetts state representative where he served on the powerful House Ways and Means Committee and never missed a roll call, casting more than 1,000 consecutive votes. In 1998, Guerriero was elected mayor of the city of Melrose, Massachusetts where he served two terms, winning reelection with more than 80 percent of the vote. In 2002, after serving as then-Governor Jane M. Swift's deputy chief of staff, Guerriero became the nation's first openly gay candidate for lieutenant governor when he was chosen by Swift to be her running mate.