The 2017–18 NIFL Championship was the second season of the second-tier Irish League since gaining senior status.
Warrenpoint Town were champions in the previous season and were promoted to the 2017–18 NIFL Premiership.
Runners-up Institute won 3–2 on aggregate in the promotion pre-play-off against third-placed Ballyclare Comrades, but were defeated 5–2 on aggregate by Carrick Rangers in the Premiership play-off, therefore remaining in the Championship for this season.
The bottom team from the previous season, Annagh United, were relegated to the third-tier NIFL Premier Intermediate League.
They were replaced by Limavady United, winners of the Premier Intermediate League.