John Denis Browne, 1st Marquess of Sligo, KP, PC (Ire) (11 June 1756 – 2 January 1809) was an Anglo-Irish peer, absentee slaveholder and politician, and was the son of Peter Browne, 2nd Earl of Altamont, and his wife Elizabeth, née Kelly, heiress and daughter of Denis Kelly, Chief Justice of Jamaica.

Peter's marriage to Elizabeth led to the family inheriting the Kelly's slave plantations in Jamaica.

Browne represented Jamestown in the Irish House of Commons from 1776 to 1780, when he succeeded as Earl of Altamont.

He became Marquess of Sligo on 29 December 1800 and was appointed a Knight of the Order of St Patrick on 5 August 1800.

A great-grandnephew was the British composer and poet, William Charles Denis Browne (1888–1915).