In 1836, an Act of Parliament was passed granting the Ulster Railway Company licence to "lay a line of rails from the town of Belfast to the city of Armagh". Radiating from its Great Victoria Street station in Belfast, which was both the terminus and headquarters of the company, the first train rolled into Lisburn on 12 August 1839. Trains first ran into Lurgan on 18th November 1841 and on 31st January 1842 a temporary terminus was brought into operation at Seagoe on the outskirts of Portadown. Because of the soft nature of the ground it was not until 12th September 1842 that the Ulster made it to its new station at Watson Street, Portadown.

The engineers involved were a distinguished trio: William Bald, who directed the project, was the designer of the Antrim Coast Road; John Godwin, engineer, had trained under Sir James McAdam, and William Dargan, the contractor, had worked under the famous Thomas Telford.

Portadown was to pose yet another challenge in the form of the River Bann and the need to construct a bridge over it resulted in the first trains not rolling into Armagh until 1848. It was not until 1852 following completion of the viaduct at Bessbrook that the line from Portadown was built through to just north of Drogheda. Dublin was finally reached in 1855 after a bridge over the River Boyne was completed. The Armagh line was subsequently extended to Clones in 1863 and, from there on to Enniskillen. Another railway line, which opened in 1858, radiated from Portadown towards Omagh via Dungannon and was operated by the “Portadown, Dungannon and Omagh Junction Company”. These three lines firmly established Portadown as a major railway junction.