Brought up with his elder brother Thomas Percy, 7th Earl of Northumberland (1528–1572), he took part as a youth in border warfare, and on Queen Mary's accession was appointed governor of Tynemouth Castle.

He was returned to the House of Commons in 1554 as Member of Parliament for Morpeth, Northumberland, was knighted in 1557, and became deputy warden of the east and middle marches.

When war broke out in Scotland in 1560, he was given the command of a body of light horse, to be equipped like the Reiter with corselets and two pistols each, and at the head of these troops he distinguished himself before Leith (April 1560).

He had already (24 June 1559) been commissioned, together with Thomas Young, Archbishop of York, to administer the oath of supremacy to the clergy of the northern province.

[1] During the Rising of the North, in which his elder brother was a chief actor (November–December 1569), Henry Percy remained loyal to the government, joined the royal forces, and vigorously attacked the rebels.

Mary, Queen of Scots, was in confinement at Tutbury, and he opened communication with her agent John Lesley, the bishop of Ross, at Easter 1571, offering help for her escape.

In September 1582 he entertained the French agent, M. de Bex, and looked with a friendly eye on Throckmorton's plot to release Queen Mary.

Immediately after his death there was published at Cologne a tract, entitled Crudelitatis Calvinianae Exempla duo recentissima ex Anglia, in which the English government was charged both with Northumberland's murder and with the enforcement of the penal statutes passed in the previous year.

To allay the public excitement, a Star Chamber inquiry was ordered, and it was held on 23 June; A True and Summarie Reporte of the proceedings was published, and the verdict of suicide upheld.