The league consisted of 16 teams, and Glentoran won the championship.
Omagh Town were relegated after finishing bottom of the table and subsequently dissolved on 7 June 2005 owing to financial problems.
Crusaders were relegated after a 3-1 defeat on aggregate to Glenavon in the promotion play-off.
Crusaders, the club that finished in the relegation play-off place, faced Glenavon, the runners-up of the 2004–05 Irish First Division in a two-legged tie for a place in next season's Irish Premier League.
Glenavon won 3–2 on aggregate and were promoted, Crusaders were relegated.