First elected to the Riverside City Council to represent Ward 1 in 2007, Gardner was reelected in 2011. He served on the city of Riverside Community Police Review Commission from 2000–2006. He is also a longtime volunteer with the Riverside Fire Department.
Professionally, Gardner was director of sales and marketing at USAFact from 2006–2007, operations manager at Archive Management Services from 2004–2006 and production manager at The ARC of Riverside County from 2003–2004. He previously held several positions with Southern California Edison from 1973–1996.