| Irish Cup | |
| Year: | 1920–21 |
| Country: |  Ireland |
| Num Teams: | 12 |
| Defending Champions: | Shelbourne |
| Winners: | Glentoran (3rd win) |
| Second: | Glenavon |
| Matches: | 13 |
| Goals: | 26 |
| Prev Season: | 1919–20 |
| Next Season: | 1921–22 |
The 1920–21 Irish Cup was the 41st edition of the Irish Cup, the premier knock-out cup competition in Irish football.
Glentoran won the tournament for the 3rd time, defeating Glenavon 2–0 in the final at Windsor Park.[1] [2] This was the final tournament organised on an all-Ireland basis as the partition of Ireland process began in May 1921, and the FAI Cup was subsequently founded as an equivalent cup competition for teams in Southern Ireland (present-day Republic of Ireland).
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1Glenavon advanced into the final after Shelbourne refused to play on 17 March which was set as the semi-final replay date.