Henry Percy, 3rd Earl of Northumberland, (25 July 1421 – 29 March 1461) was the son of Henry Percy, 2nd Earl of Northumberland and Lady Eleanor Neville, daughter of Ralph Neville, 1st Earl of Westmorland and his second wife Joan Beaufort.
His maternal uncles included Richard Neville, 5th Earl of Salisbury. His maternal aunts included Cecily Neville. Percy was first cousin to (among others) Edward IV of England, Margaret of Burgundy, George, Duke of Clarence and Richard III of England. He was thus closely related to the House of York.
Percy however followed his father in swearing allegiance to the House of Lancaster. On December 30, 1460, Percy is known to have fought on the Lancastrian side at the Battle of Wakefield. He commanded the Lancastrian van at the Battle of Towton, where he was killed.

Marriage and children
He was married to Eleanor Poynings (1422-1480) , daughter of Richard Poynings, Lord Poynings. They had the following children:

Ralph Percy (b. 1440), died young.
Lady Anne Percy (1444-1522), married 1. Sir Thomas Hungerford; 2. Sir Laurence Rainsford; 3. Sir Thomas Vaughn.
Lady Margaret Percy (b. 1447), married Sir William "the younger" Gascoigne.
Henry Percy, 4th Earl of Northumberland (1449-1489), married Lady Maud Herbert.
Lady Eleanor Percy (b. 1455), married Thomas West, 8th Baron De La Warr.
Lady Elizabeth Percy (1460-1512), married Henry Scrope, 6th Baron Scrope of Bolton.
Lady Mary Percy, died young.