The 2020–21 season is Grimsby Town's 143rd in existence and their fifth consecutive season in EFL League Two. Along with competing in League Two, the club will also participate in the FA Cup, EFL Cup and EFL Trophy. The season covers the period from 1 July 2020 to 30 June 2021. The team struggled through the course of the season with relegation to the National League confirmed on April 27 after a 3-2 loss to Exeter City F.C.