[3] In 1790 he acted as the election agent for Robert Stewart, the future Lord Castlereagh, when he successfully stood for the County Down constituency of the Irish Parliament.

Samuel Neilson was a driving force on the ground in Ireland, helping organise groups of Irishmen as soldiers in the battle of gaining independence from Britain.

In March 1798, information of a meeting of the United Irish executive at the house of Oliver Bond led to the arrest of most of the leadership, leaving Neilson and Lord Edward Fitzgerald the only figures of national importance still at liberty.

Opposed by the Sheares brothers, who were working to subvert the conscript militia and to initiate a coup, they decided to press ahead as soon as possible and on the basis of the movement's own resources.

[6] As the date, finally set for 23 May, loomed closer, the authorities went into overdrive to sweep up the rump leadership, and on 18 May Lord Edward was betrayed in his hiding place and critically wounded while resisting capture.

[3] After the execution of John and Henry Sheares, Neilson and the remaining prisoners agreed to provide the authorities with details of the organisation of the United Irishmen and plans for the rebellion in exchange for a sentence of exile.

Neilson was preparing to revive the Northern Star and bring his family over from Ireland when an outbreak of yellow fever struck the city in August 1803.