The Great Northern Railway (Ireland) (GNR(I) or GNRI) was an Irish gauge (1,600 mm (5 ft 3 in)) railway company in Ireland. It was formed in 1876 by a merger of the Irish North Western Railway (INW), Northern Railway of Ireland, and Ulster Railway. The governments of Ireland and Northern Ireland jointly nationalised the company in 1953, and the company was liquidated in 1958: assets were split on national lines between the Ulster Transport Authority and Córas Iompair Éireann.

The Ulster Railway was a railway company operating in Ulster, Ireland. The company was incorporated in 1836 and merged with two other railway companies in 1876 to form the Great Northern Railway (Ireland).