John IV of Montfort (in French Jean IV de Montfort) (1295 - September 16 1345), was duke of Brittany, from 1341 to his death. He was son of Duke Arthur II and Yolande de Dreux, countess of Montfort, his second wife. From his mother he became count of Montfort.

When his half-brother, duke John III, died with no male heirs in 1341, John decided to fight the rights of his niece Joanna of Dreux and her husband Charles of Blois to the duchy of Brittany. This lead to the Breton War of Succession an event of the Hundred Years War. His patron on this quest was king Edward III of England. John IV died without accomplishing his objective of becoming sole ruler of Brittany, but his wife Joanna of Flanders continued the fight in the name of their son John V who eventually won the Succession War.

See also

• Dukes of Brittany family tree

Preceded by: John III

Duke of Brittany disputed with Joanna and Charles

Succeeded by: John V