Mullingar, county town of Westmeath, was first served by rail when the Midland Great Western Railway opened their mainline from Dublin to here in 1848. The MGWR then extended their Galway line west from Mullingar to Athlone, while the town of Sligo had to wait until its construction to Longford in 1855, and Sligo itself in 1862. Galway & Mayo line services were diverted via Portlarlington on the rival Great Southern & Western's mainline from Dublin after 1973, with the last scheduled train traversing the Mullingar to Athlone line in 1987. This line was used by freight and ballast movements up until the late 1990s, but today only engineering trains have traversed it in recent years.

Mullingar Station is of a 'V' shaped design, with the station buildings, complete with original canopies located in the centre, along with the large signal cabin, one of original three in Mullingar. The Sligo side of the station retains its up & down platforms, along with a bay for commuter trains. In 2003 the complex trackwork at the east end of the station where the Athlone line diverges was rationalised and now only the disused up platform on the Galway side of the station can be of use, the down line having been turned into a siding. The former loco sheds and turntable at the western yard in Mullingar is now used by the RPSI coach department. Even further west can be found the engineers track & ballast loading point adjacent to the semi-disused Athlone line.