Percy Hamilton Seymour, 18th Duke of Somerset (27 September 1910 – 15 November 1984), styled Lord Seymour between 1931 and 1954, of Bradley House in the parish of Maiden Bradley, Wiltshire, was a British peer.

He was the son of Evelyn Seymour, 17th Duke of Somerset by his wife Edith Parker, a daughter of William Parker by his wife Lucinda Steeves (a daughter of William Steeves, one of the Fathers of Canadian Confederation).^[1]

He was educated at Blundell's School, Tiverton in Devon, and at Clare College, Cambridge.^[1]

After Cambridge, he was commissioned into the Wiltshire Regiment. He saw service in India, Persia and Burma.^[1]

In London on 18 December 1951, he married Gwendoline Collette Jane Thomas (d. 18 February 2005, aged 91), daughter of Major John Cyril Collette Thomas, of Burn Cottage, Bude, Cornwall, by whom he had three children:^[1]

• John Michael Edward Seymour, 19th Duke of Somerset (b. 1952), who married Judith-Rose Hull, daughter of John Folliott Hull, in 1978.^[1]
• Lady Anne Frances Mary Seymour (b. 1954), unmarried and without issue.^[1]
• Lord Francis Charles Edward Seymour (b. 1956), who married Paddy Poynder, daughter of Colonel Anthony John Irvine Tony Poynder, MC, Corps of Royal Engineers, in 1982.^[1]

The 18th Duke died on 15 November 1984 at Warminster, Wiltshire and was succeeded in his titles by his elder son, John.^[2]