The 2012 League of Ireland First Division season was the 28th season of the League of Ireland First Division. The First Division was contested by 8 teams and Limerick won the title.
Due to the expansion of the Premier Division, coupled with the withdrawal of Galway United during the off-season, the 2012 First Division consisted of just eight teams. Applications to join the Division from Cobh Ramblers and Tralee Dynamos, both of whom had played in the 2011 A Championship, were rejected. Each team played every other team four times, totalling twenty eight games.[2][3]
Dundalk win 4–2 on aggregate and retained their place in the Premier Division. Waterford United appealed the result of the playoff, claiming Michael Rafter was ineligible as Dundalk had incorrectly registered him when they signed him earlier that season. However the appeal was unsuccessful.[8][9][10]