The 1990–91 Irish Cup was the 111th edition of the Irish Cup, Northern Ireland's premier football knock-out cup competition. It concluded on 4 May 1991 with the final.[1]
Glentoran were the defending champions after winning their 15th Irish Cup last season, defeating Portadown 3–0 in the 1990 final.[2] This season Portadown went one better by winning their first Irish cup in their fifth appearance in the final. They defeated Glenavon 2–1 in the final.[3]