Samuel Neilson (17 September 1761 – 29 August 1803) was one of the founder members of the Society of United Irishmen and the founder of its newspaper the Northern Star.
Neilson was born in Ballyroney, County Down, Ireland, the son of Presbyterian minister Alexander, and Agnes Neilson. He was educated locally. Samuel was the second son in a family of eight sons and five daughters. At 16 years of age, Samuel was apprenticed to his elder brother, John, in the business of woollen drapery in Belfast. At the age of 24 he established his own business.
Despite his commercial success, Neilson was naturally drawn to politics and had early on been a member of the reformist Volunteer movement. In 1791, inspired by the French Revolution, he suggested to Henry Joy McCracken the idea of a political society of Irishmen of every religious persuasion. He tone was not a founder member) established the United Irishmen in Belfast. The following year he launched the newspaper of the United Irishmen, the Northern Star, which effectively threw away his fortune. As its editor he was a high-profile target for the authorities and was prosecuted for libel several times, being twice imprisoned between 1796-98.
Along with several other "state prisoners" (persons imprisoned indefinitely without charge) Neilson was released in February 1798 following several petitions by influential friends, on grounds of bad health. Upon release he immediately involved himself in the United Irishmen aligning with the radicals among the leadership who were pressing for immediate rebellion and opposed to the moderates who wished to wait for French assistance before acting.
The United Irishmen were however, severely penetrated by informers who kept Dublin Castle abreast of their plans and discussions. 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 as the only figures of national importance still at liberty. They decided to press ahead as soon as possible and settled on 23 May as the date for the rebellion to begin.