Carroll was re-elected without opposition in 2008. In advance of the 2011 legislative session, he unsuccessfully ran for the open position of Senate Democratic floor leader, losing to R. J. Palmer of Winchester. Carroll blamed his contentious relationship with Senate President David L. Williams as the reason his colleagues were hesitant to choose him for the post. On November 6, 2012, he defeated Republican Frank Haynes to retain his seat for another four years. He was re-elected without opposition in 2016 from a district now comprising Anderson, Woodford, Franklin, Owen and Gallatin counties.