The 1920–21 Irish League was the 27th edition of the Irish League, the highest level of league competition in Irish football. The league comprised 5 teams, and Glentoran won the championship.
Although the Dublin-based teams that had competed the previous season had withdrawn from the league for this edition, this was the final season in which the Irish Football Association/Irish League had jurisdiction over the entire island of Ireland. The partition of Ireland process began in May 1921, and the League of Ireland was subsequently founded as an equivalent league competition for teams in Southern Ireland (present-day Republic of Ireland) for the following season.
The Irish League continued as the highest level of league competition solely for teams based in Northern Ireland.
