Browne was the second son of two sons and four daughters born to
Peter Browne, 2nd Earl of Altamont and Elizabeth Kelly of Lisduffe,
County Galway. He was born and raised at the family home of
Westport House,
County Mayo. He was a direct descendant of the
pirate,
Grace O'Malley (c.1530-c.1603). The Browne Family being one of the ancient
Tribes of Galway and had been originally
Catholic before conversion to the
Church of Ireland. Most of the family property was left to John Denis, a sum of £5000 and a life interest in the property of Mount Browne were granted to Denis Browne. Denis Browne purchased the Claremont estate from Dominic Browne of Castlemacgarrett. Browne served as an officer in the
5th Royal Irish Dragoons from 1779 to 1784. Due to his brother's influence and the support of the Irish catholic interest, he was elected MP for
County Mayo in 1782, which he would hold till 1800. His uncle,
James Browne, Prime Sergeant, was dismissed in 1782 which led to the brothers going into opposition against the government. In time, they were conciliated by the
Duke of Rutland's administration. Browne was appointed to the
Privy council on 20 January 1794. Browne supported
Catholic emancipation but would not help the Catholic Committee in organising elections in the county;
Wolfe Tone believed this was because Browne was unwilling to lose any influence in his locality. On the other hand, Browne and his brother supported the government, keeping the administration in
Dublin well informed of events in Mayo in the years prior to the
Irish Rebellion of 1798. In 1795 Browne and his brother Lord Altamount assisted over five hundred Ulster families who fled to Mayo in the wake of disturbances arising from the
Battle of the Diamond. All the refugees were carefully questioned to root out any disaffected elements, the families settling on the family estates. He was appointed
High Sheriff of Mayo for 1798, the year of the
Irish Rebellion. During this time his home in
Claremorris was destroyed by the rebels. Browne had a well-earned reputation as a feared duelist. While Sheriff, he fought against
George Robert FitzGerald; another, during the election of 1790, against his electoral opponent, John Bingham. In 1801 he fought against another parliamentary opponent, won, and was returned unopposed for
County Mayo. Browne's subsequent support for the
Acts of Union 1800 failed to gain him a
peerage, though his brother was made first
Marquess of Sligo. In the following decades he represented
Mayo (1800–1818) and
Kilkenny City (1820–26), strongly supporting military coercion in Ireland. ==Public Opinion in Ireland==