The 2019–20 season was Millwall's 135th year in existence, 93rd consecutive season in The Football League, and 43rd in the second tier. Millwall competed in the Championship, FA Cup, and League Cup. Millwall manager Neil Harris resigned ten games into the season, on 3 October 2019. He was in charge of the club for four and a half years. Gary Rowett took over as manager on 21 October. The Championship season was suspended due to the COVID-19 Pandemic on 13 March 2020. After measures were put in place to make playing games safe, such as playing games behind closed doors with no fans, and rounds of testing for players it was decided to restart the season. Millwall resumed against Derby County on 20 June 2020. The season covered the period between 1 July 2019 and 22 July 2020.