2003–04 Irish First Division

The 2003–04 Irish First Division was the ninth season of second-tier football in Northern Ireland under the league system at the time. The division consisted of 12 clubs.

Loughgall were the champions and were promoted to the 2004–05 Irish Premier League. Armagh City finished second and entered the promotion play-off, losing to Cliftonville 4–1 on aggregate. Lurgan Celtic and Brantwood were relegated to the Irish Second Division.