Henry Haslett (1758 – 1806) was in 1791 a founding member in Belfast of the democratic-revolutionary Society of the United Irishmen, and one of the twelve original proprietors of its Painite newspaper, the Northern Star.

Born in Limavady, in Belfast Haslett initially set up business as a woollen draper but soon diversified with investments in Whitbread Porter, shipping and insurance.

The Volunteers formed in the American War as a reserve militia in the event of a French invasion, mobilised Protestants but, more especially in the north of Ireland, Presbyterians in opposition to the landed Ascendancy and its deference to English interests represented by the government of the London-appointed Lord Lieutenant.

He shared in the general patriotic enthusiasm for liberties seen as secured in America through independence, in France by the Revolution, and vindicated in Thomas Paine's Rights of Man.

In September 1796, Haslett was arrested along with Russell and Neilson, understood by the Lord Lieutenant, Earl Camden to be "the most leading characters in Belfast" and "all men of abilitys".

In spite of having done much to counsel moderation and calm tensions in his native Limavady and Roe Valley, he was again arrested and held until December 1799[7] After his release from prison, Haslett, possibly to allay suspicion, made a public donation to the loyalist Belfast yeomanry.