Harðarson became interim head coach at IK Start, after Kjetil Rekdal left the position in April 2019. On 10 July 2019, Start announced that Harðarson would coach the team for the rest of the season. On 23 October2019, Start announced that Joey Harðarson had agreed to a contract as head coach on permanent basis till the end of the 2021 season. Start finished the 2019 season in third place and qualified for promotion play-offs. Harðarson's Start won promotion to Eliteserien on the away goals rule after a 5–5 draw on aggregate against Lillestrøm in the play-off final. He was sacked on 14 June 2021.