The 1890–91 Irish Cup was the 11th edition of the Irish Cup, the premier knock-out cup competition in Irish football.
Linfield won the tournament for the 1st time, defeating Ulster 4–2 in the final.
[1][2] 1 Match ordered to be replayed after Black Watch protested it was too dark to finish the match.
[2] 1 Match was ordered to be replayed on the grounds that no touchline had been drawn.
[2] 2 Cliftonville scratched (withdrew) after claiming that the ordering of a replay with 24 hours notice did not give them enough time to prepare.