John Anthony William Gardner (born 9 February 1979) is a former Australian Liberal politician who represented the seat of Morialta in the South Australian House of Assembly from 2010 until his defeat at the 2026 election. Gardner served as the Minister for Education in the Marshall ministry between March 2018 and March 2022.
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. He increased his two-party vote to 60 percent at the 2014 election.
Gardner had previously been a senior staffer for Christopher Pyne, Liberal MP for the federal seat of Sturt. Gardner lives in his childhood suburb of Rostrevor within the electorate of Morialta.
In January 2016 Gardner was appointed Shadow Minister for Education, Multicultural affairs and Arts.
After Deputy Liberal Leader Dan van Holst Pellekaan lost his seat at the 2022 South Australian state election, Gardner was elected Deputy Leader in his place, and hence Deputy Leader of the Opposition.