The 2009–10 season was the 115th season in the history of Plymouth Argyle Football Club, their 85th in the Football League, and 41st in the second tier of the English football league system. Their 21st-place finish in the 2008–09 season meant it was their sixth successive season playing in the Championship. Their campaign ended disappointingly as they were relegated to League One with 11 wins, 8 draws, and 27 losses from 46 matches. The club exited both domestic cup competitions at the first stage, being eliminated by Newcastle United in the third round of the FA Cup and by Gillingham in the first round of the League Cup. The club changed managers in December due to a string of poor results as Paul Sturrock was replaced by Paul Mariner.

Damien Michael Johnson is a Northern Irish football coach and former international player. Since 2019 he has been first team technical coach & head of player development at Blackburn Rovers.