[1][2] Henry was born at Althorp to William Spencer, 2nd Baron Spencer of Wormleighton and Lady Penelope Wriothesley, daughter of Henry Wriothesley, 3rd Earl of Southampton, and was baptised on 23 November 1620 at Great Brington church.

He attended Magdalen College, Oxford and graduated from there with a Master of Arts degree on 31 August 1636.

It was generally believed to be a love marriage and had his father-in-law's warm approval: after Sunderland's death, her father consoled Dorothy by reminding her of her happy marriage, which he was happy to have helped bring about.

[2] He then fought in the Siege of Gloucester in August 1643 and the First Battle of Newbury on 20 September 1643, where he was killed, aged 22, by a cannonball.

[2] Cokayne writes that "he was, according to Clarendon, a lord of a great fortune, tender years ... and an early judgment; who, having no command in the army, attended upon the King's person under the obligation of honour; and putting himself that day into the King's troop a volunteer, before they came to charge was taken away by a cannon bullet.