The 1983–84 season was the 69th season of the Isthmian League, an English football competition. Harrow Borough were champions, winning their first Isthmian League title. There was no promotion from the Isthmian League to the Alliance Premier League till 1985. Windsor & Eton finished first in Division One achieving the second promotion in a row. Corinthian-Casuals were excluded from the league after new groundsharing ruled were introduced.