Long was appointed High Sheriff of Wiltshire in 1512, 1526, 1536 and 1542, and for Dorset 1539. He was High Sheriff of Somerset in 1538 and Member of Parliament for Wiltshire 1552-1553. He was also Hereditary Bailiff of Charlton Wood and Keeper of Braden Forest, east of Malmesbury. Together with his brother Richard, he was present at the baptism of Prince Edward.
He inherited the manor of Stock & Stockley from his father and later purchased the manor of South Wraxall. Long was at the Siege of Boulogne, having the command of 200 men, whom he railed for that expedition. His Captain was severely wounded in an unsuccessful attack on the castle, 1 September 1544. He also accompanied Henry VIII to the Field of the Cloth of Gold and was knighted for making a gallant charge at Therouenne at Picardy in the sight of the King, for which he was granted a new crest, consisting of a lions head with a man's hand in its mouth.
Long's close relationship with Henry VIII paid dividends at the Dissolution of the Monasteries, with grants of land in Wiltshire; Lyneham and Littlecote in Hilmarton, together with the rectory, great tithes and advowson of the vicarage of Lyneham, all formerly belonging to Bradenstoke Priory. He leased the manor of Fasterne from Catherine Parr who, after the death of her husband Henry VIII, had re-married Sir Thomas Seymour, brother of Protector Somerset. The Protector coveted Fasterne, and negotiated with Sir Henry Long to resign his lease. When she heard of this, Catherine was highly indignant. She was not on good terms with the Protector, because he had declined to give her some valuable jewels which, as she maintained, King Henry had given her for her own. She vowed she would stop the Protector getting his hands on the Fasterne lease, and would go herself "tomorrow, Saturday, at three o’clock" to the young King Edward, and give full utterance to her feelings against the Protector, his uncle. But the formidable uncle-Protector of the realm was not to be meddled with. Whether she kept her promise, and how far she succeeded in getting the diamonds, is not clear, but Somerset succeeded in getting Fasterne. Sir Henry Long somewhat unwillingly parted with it for a sum of money and the office of Ranger of Braden Forest for his life.
Long married firstly, Jane (or Frydeswyde), daughter of Sir John Hungerford and Margaret Blount. He married secondly, Eleanor, daughter of Sir Richard Wrottesley and Dorothy Sutton. He had several children with both his wives, including Sir Robert Long. Sir Henry Long died c.1556 and is buried at Draycot in Wiltshire. His second wife died c.1543.