Shortly after his playing career ended, Gardner jumped into the coaching profession, becoming head coach of the Newmarket Saints of the American Hockey League for four seasons. He would later become an assistant coach for the Baltimore Skipjacks under coach Barry Trotz. Both Trotz and Gardner would later be promoted to the NHL level when they moved to Nashville to work for the expansion Predators. Gardner would be assistant coach through the 2002–03 season and then worked as a pro scout for the organization. In January 2007, he was named head coach of the Russian KHL team Lokomotiv Yaroslavl. He guided the team to a nine-game winning streak and made the playoffs, but was released in February 2008. In the summer of 2008, he was named head coach of Dynamo Minsk in Belarus and assistant coach of the Belarus national team. In late July 2008, his contract was cancelled due to personal reasons. On December 18, 2008, he became the coach of the Hamburg Freezers of the Deutsche Eishockey Liga and guided the Freezers to the playoff-quarterfinals that season. In Gardner's second season at the helm, Hamburg did not qualify for the playoffs. His contract expired at the end of the 2009-10 season. Gardner signed with the Mississippi RiverKings of the Central Hockey League for the 2010-11 campaign. On July 29, 2011, Gardner was informed by the team that was relieved of his duties for the following season. In September 13, 2011 Gardner was named head coach of fellow CHL team Bloomington Blaze. On January 18, 2013 Gardner was appointed head coach of the Braehead Clan of the Elite Ice Hockey League. He guided the Scottish club to the EIHL Gardiner Conference Championship and a playoff-quarterfinal appearance, but did not have his contract renewed at the end of the 2012-13 season. In Mai 2013, Gardner was named head coach of Dutch Eredivisie side Tilburg Trappers, signing a two-year deal with the team. Under his guidance, the Trappers won back-to-back Dutch championship titles and Dutch cup titles. On January 1, 2016, German second-division club Lausitzer Füchse hired Gardner as their new head coach. He stayed on the job through the end of the 2015-16 season. On June 29, 2016, Gardner took over the coaching job at fellow DEL2 side Löwen Frankfurt, working alongside sporting directorRich Chernomaz. He guided the Frankfurt team to the 2017 DEL2 title in his first year in charge. Gardner was sacked on March 17, 2018, during the playoff quarterfinal series against Kassel, in which the Frankfurt team had lost the first two games. In 2019, Gardner was inducted into the Leaside Sports Hall of Fame.