Sligo's railway story begins on 3 December 1862, when the Midland Great Western Railway extended its main line from Dublin and made the seaport a terminal. Within twenty years it became a small hub: the Sligo, Leitrim and Northern Counties Railway pushed north to Enniskillen in 1881, and in 1895 the Waterford and Limerick Railway - later the Great Southern and Western - linked Sligo to Limerick and the south. For a few decades you could board a train in Sligo and reach almost anywhere in Ireland that mattered. The Enniskillen line closed in 1957. The Limerick passenger service ended in 1963. Today only the Dublin line survives, and it survives well - regular intercity services connect the northwest to the capital in just over three hours.

In 1966, on the fiftieth anniversary of the Easter Rising, the station was renamed Mac Diarmada Station after Seán Mac Diarmada from County Leitrim. Mac Diarmada was one of the seven signatories of the 1916 Proclamation of the Irish Republic, executed by firing squad at Kilmainham Gaol on 12 May 1916. He was thirty-three. He walked with a limp from polio. He helped organise the Rising knowing that defeat was likely, and that defeat would likely cost him his life. The renaming - one of many across Ireland that year - was a deliberate act of public memory. The locals largely just call it Sligo Station, which is fine. Mac Diarmada's name is still on the signs.

When the Midland Great Western Railway came to Sligo in 1862, it also built a short branch curving off north and downward before reaching the station, dropping to the freight terminal at Sligo Quay. A large crane built by CIÉ in the mid-1970s handled containers there. The last freight train left Sligo Quay in December 2008, ending more than 140 years of rail freight in the town. The track is still there. The crane is still there. On 1 December 2021, Iarnród Éireann's Rail Freight 2040 strategy named Sligo as one of three future Tactical Rail Freight Terminals, alongside Galway and Cork - a hopeful sign that the dormant freight line might one day wake again, moving regional goods back onto rails for the first time in nearly two decades.

The current station building, opened after the 1923 fire, sits raised above the surrounding streets, its frontage dominating the approach from Lord Edward Street. Two platforms, one intermediate carriage siding, and a passing loop on the approach handle the modest but steady traffic of the modern line. There used to be a turntable here for steam locomotives, later useful for turning the CIÉ 121 Class single-cabbed diesels that worked the route in the latter half of the twentieth century. The locomotive shed to the south of the line is long gone, demolished. The bus station sits at street level adjacent to the south side - the two services share a small interchange that handles most onward connections in the northwest. Sligo Mac Diarmada is the end of the line, in the literal sense. Further west, there is only the bay.