The 2020–21 season was Millwall's 136th year in existence, 94th consecutive season in the Football League, and 44th in the second tier. Millwall competed in the Championship for the fourth consecutive season and finished in 11th place. They also played in the FA Cup where they reached the fourth round, and the League Cup where they reached the third round. This season marked the first time in Millwall's history that they played more seasons in the second tier (44) than the third tier (43).