Romanoff was a member of the Colorado House of Representatives from 2000 to 2008, winning re-election three times. Romanoff became Speaker of the House in 2005, and at the time was the youngest speaker in the history of the Colorado House. Before becoming speaker he was the House Minority Leader, representing House District 6. Romanoff was considered by many to be a possible Democratic candidate for Governor of Colorado in 2006, but announced in late 2005 that he would not seek the Democratic nomination for governor. Romanoff left the Colorado House after 2008 due to term limits.