[2][3] The new seat of Morialta to replace Coles was won by Liberal incumbent Joan Hall on a two-party vote of 54.1 percent at the 2002 election.

Labor's Lindsay Simmons defeated Hall at the 2006 election with 57.9 percent of the two-party vote, an 11.2-point post-redistribution swing.

Gardner defeated Simmons at the 2010 election, receiving 54.1 percent of the two-party vote, an 11.1-point post-redistribution swing.

Gardner had previously been a senior staffer for Christopher Pyne, Liberal MP for the federal seat of Sturt.

In January 2016 Gardner was appointed Shadow Minister for Education, Multicultural affairs and Arts.