Cartwright was first elected to Pennsylvania's 17th Congressional District in 2012. Prior to joining Congress, he worked as a lawyer with the firm Munley, Munley & Cartwright for 25 years.
At the start of the 116th Congress, Cartwright was one of four Democrats selected to lead the Democratic Policy and Communications Committee. According to The Morning Call, this committee is responsible for developing messaging related to the agenda and positions of the Democratic Party, and is often used as a stepping stone to other leadership positions within the Democratic caucus. Cartwright is a member of the communist-dominated Congressional Progressive Caucus and a sponsor of the Medicare for All bill.