Ruiz ran for the United States House of Representatives in 2012 as a first-time candidate in . The district had previously been the 45th, represented by 15-year incumbent Mary Bono Mack and previously by her late husband Sonny Bono. Ruiz was initially regarded as a long shot to win. He was endorsed by Bill Clinton in October 2012. The new district was significantly more Latino than its predecessor; Latinos now made up almost half its population. Ruiz appealed to them by running Spanish-language ads. He was elected with 52.9% of the vote, to Bono Mack's 47.1%.