John V (in French Jean V) (1339 - November 1 1399), known as the Conqueror, was duke of Brittany, from 1345 to his death. He was son of Duke John IV and Joanna of Flanders.

The first part of his rule was tainted by the Breton War of Succession, fought against his cousin Joanna of Dreux and her husband Charles of Blois. In 1364, John V managed to win an important victory against the House of Blois in the battle of Auray, with the help of the English army. His rival Charles was killed in battle and Joanna forced to sign the Treaty Guérande in April 12 1365. In the terms of the treaty, Joanna gives up her rights to Brittany and recognizes John V as sole master of the duchy. Surprisingly, John V declares himself a vassal to king Charles V of France, not to Edward III of England who helped him to become duke. Nevertheless, the French exerted pressure over Brittany and the local nobles and forced John V to exile between 1373 and 1379.

John V married three times: 1) princess Mary of England (1344-1362), daughter of Edward III; 2) Joanna of Holland, countess of Kent (1350-1384) and 3) princess Joanna of Navarre (1370-1437), daughter of king Charles II, the mother of his children.

See also: Dukes of Brittany family tree