Sir Guy de Bryan, KG (born before 1319, died 17 August 1390) was an English soldier, the son of Sir Guy de Bryan or Brienne, of Walwyn's Castle in Pembrokeshire and Torbryan in Devon. He succeeded his father in 1349.
He served on the English side in the Second War of Scottish Independence and in France and Flanders during the Hundred Years' War. In 1341 he was made Governor of St Briavel's Castle and Warden of the Forest of Dean, offices he held until his death. In 1349 he was temporarily Keeper of the Great Seal of England, and in 1350 was granted an annuity of 200 marks for bearing the King's Standard against the French at Calais. From 25 November 1350 he was summoned to Parliament and may thereby be held to have been created Baron Bryan. In 1361 he was Ambassador to the Pope, and in 1369 Admiral of the Fleet. Following the death of Sir John Chandos on 31 December 1369 he was made a Knight of the Garter.
He married firstly, before 1348, Joan, daughter of Sir John Carew of Carew. His second wife, whom he married before 10 July 1350, was Elizabeth, widow of Hugh le Despencer, 2nd Baron le Despencer and of Giles de Badlesmere, 2nd Baron Badlesmere, and daughter of William Montagu, 1st Earl of Salisbury and Catherine Grandison. By his second wife he is known to have had three sons and a daughter, along with at least one other child:
Lady Bryan died on 31 May 1359 and Lord Bryan on 17 August 1390. They were both buried in Tewkesbury Abbey. His executrix was his daughter-in-law Alice and his co-heiresses were his granddaughters Phillipe (age 12) and Elizabeth (age 10). Any right to the Barony of Bryan is presumed to have become extinct on the death of his great-great-granddaughter Avice, Countess of Ormonde, in 1457.