Kilmorey was the third son of John Needham, 10th Viscount Kilmorey, and Anne (née Hurleston), daughter and co-heiress of John Hurleston, of Newton.

[1] He entered the British Army in 1762 and served in the American War of Independence, where he was taken prisoner at the Siege of Yorktown in 1781.

He also fought in the French Revolutionary Wars but is best remembered for his role during the Irish Rebellion of 1798.

He succeeded his elder brother in the viscountcy in 1818 but as this was an Irish peerage it did not entitle him to a seat in the House of Lords.

In 1822 he was honoured when he was made Viscount Newry and Mourne, in the County of Down, and Earl of Kilmorey.