Guinta worked in the insurance industry before being elected to the New Hampshire House of Representatives, where he served from 2000 to 2004; he also served as a Manchester alderman from 2001 to 2005. He resigned from the State House in 2004 to work as senior policy adviser to Republican Congressman Jeb Bradley. In 2005, he ran for mayor of Manchester and defeated three-term Democratic incumbent Robert A. Baines. He was re-elected in 2007 but did not run for a third term in 2009. Instead, he ran for Congress in 2010, defeating Democratic incumbent Carol Shea-Porter. In a rematch in 2012, Shea-Porter defeated Guinta to reclaim the seat. Guinta defeated Shea-Porter for a second time in 2014. Shea-Porter defeated Guinta on November 8, 2016, to win back the seat.