Newry City will play Linfield in the Irish Cup semi-final on 31 March after winning their case over the eligibility of Ballymena player Alan Davidson.
Last week, the Irish FA's cup committee had rejected a protest, despite Newry pointing out that Ballymena had signed Davidson after the 31 January deadline.
However, on Monday night the IFA's Appeals Board overturned that ruling.
Davidson, who joined Ballymena in February, scored the winner when United beat Newry 2-1 in the quarter-finals.
A statement from the association read: "After a lengthy and detailed consideration of the submissions made by Newry City and the IFA Challenge Cup Committee, the Appeals Board unanimously upheld the appeal of Newry and found that Ballymena United's Alan Davidson was not eligible to play in the match. Newry City are therefore reinstated into the 2012 JJB Sports Irish Cup."
When the original protest by Newry was turned down, the Challenge Cup committee said it was felt the cup's rules had to be read in parallel with the IFA Premiership Rules and Fifa regulations covering the status and transfer of players.
Davidson's registration with his previous club, Glenavon, was cancelled on 3 January and Ballymena registered him on 28 February.
A statement released by Newry City said they believed that Monday evening's judgement was "the correct decision not only for football and the Challenge Cup, but also to uphold the integrity of the game".
"The club would like to thank our Chairman, Management Committee and John Turley of Tughans Solicitors for all their hard work in stating our case to the Appeals Board and we now look forward to facing Linfield in the semi-final of the Irish Cup on Saturday March 31."