John was born in March 1340, the son of Edward III, king of England, and Philippa of Holland and Hainault. He was born in Ghent in Flanders, from which his name John of Gaunt derives. Aged nineteen, he married his cousin Blanche, heiress of Lancaster, daughter of Henry, duke of Lancaster, and Isabel de Beaumont. They had seven children of whom a son Henry (the future Henry IV, king of England) and two daughters would have progeny. When her father died in 1362, John became duke of Lancaster and the greatest landholder in England.
John joined his brother Edward, prince of Wales (the 'Black Prince'), on his Spanish campaign to reinstate Pedro III 'the Cruel', king of Castile, who had been deposed by his half-brother Enrique de Trastámara. After Blanche died in 1369, John married Constance, daughter of Pedro 'the Cruel', and in 1372 he claimed the Castilian crown in his wife's right, as Enrique de Trastámara had murdered her father in 1369.
In the early 1370s he campaigned against the French around La Rochelle and Bordeaux, returning to England in 1375. There he supported the court faction led by Alice Perrers, his father's mistress. Widespread opposition to Alice led to the Good Parliament of 1376 that ousted her and her followers, but John was able to reverse most of its decrees in 1377.
In an effort to undermine his clerical opponents, he supported John Wycliffe's anti-clerical theology and defended Wycliffe during his trial in 1377. During the Peasants' Revolt of 1381, the rebels sacked and burned the Savoy Palace, his London home.
In 1386 John left England to try to win the Castilian throne, but he was unsuccessful. In 1388 he relinquished his claims to his daughter Catherine, who was then married to the future Enrique III of Castile.
On his return to England in 1389, he acted as peacemaker between his nephew King Richard II and the lords appellant. However his appointment as duke of Aquitaine in 1390 revived the barons' hostility. In 1394 his second wife Constance died, and in 1396 he married his longstanding mistress Catherine Swynford. In his last years his relationship with the king became increasingly strained, and in 1398 Richard II exiled John's son Henry Bolingbroke (later Henry IV). John died on 3 February 1399 in Leicester Castle.