The Midland Great Western Railway line to Mullingar from Dublin opened in stages from 1846 to 1848, arriving in Mullingar on 2 October 1848. This was to a temporary station, adjacent to the greyhound stadium. The original mainline ran from Dublin (Broadstone Station) to Galway via Mullingar, then via Moate to Athlone, the Mullingar to Galway section opening in August 1851. The present station opened with the branch line to Longford on 14 December 1855.
There were two secondary stations in Mullingar, Canal Crossing cattle bank was on the Sligo Line and on the Athlone Line, Newbrook racecourse had its own station. This was unique in that it was a two platformed station with both platforms on the Down Line.
These days, the Dublin-Sligo railway line northwest to Longford and Sligo is the mainline, Galway is accessed from Heuston Station via Portarlington and the line between Mullingar and Athlone is currently disused. Mullingar station is served by national rail company Iarnród Éireann's Arrow commuter services to Dublin and InterCity trains to/from Sligo.
The Railway Preservation Society of Ireland have a secondary base in the town. There is a photo survey of the disused Athlone Line via Moate.