John de Mowbray, 4th Baron Mowbray

John de Mowbray, 4th Baron Mowbray (24 June 1340 – 1368) was an English peer. He was slain near Constantinople while en route to the Holy Land.

John de Mowbray, born 25 June 1340 at Epworth, Lincolnshire, was the son of John de Mowbray, 3rd Baron Mowbray, of Axholme, Lincolnshire, by his second wife, Joan of Lancaster, sixth and youngest daughter of Henry, 3rd Earl of Lancaster.

He and twenty-six others were knighted by Edward III in July 1355 while English forces were at the Downs before sailing to France. In 1356 he served in a campaign in Brittany. He had livery of his lands on 14 November 1361; however his inheritance was subject to the dower which his father had settled on his stepmother, Elizabeth de Vere. By 1369 she had married Sir William de Cossington, son and heir of Stephen de Cossington of Cossington in Aylesford, Kent; not long after the marriage she and her new husband surrendered themselves to the Fleet prison for debt. According to Archer, the cause may have been Mowbray's prosecution of his stepmother for waste of his estates; he had been awarded damages against her of almost £1000.

In about 1343 an agreement had been made for a double marriage between, on the one hand, Mowbray and Audrey Montagu, the granddaughter of Thomas of Brotherton, and on the other hand, Mowbray's sister, Blanche, and Audrey's brother, Edward Montagu. Neither marriage took place. Instead, about 1349 a double marriage was solemnized between, on the one hand, Mowbray and Elizabeth Segrave, and on the other hand, Mowbray's sister Blanche, and Elizabeth Segrave's brother John, Pope Clement VI having granted dispensations for the marriages at the request of the Earl of Lancaster in order to prevent 'disputes between the parents', who were neighbours. Mowbray had little financial benefit from his marriage during his lifetime as a result of the very large jointure which had been awarded to Elizabeth Segrave's mother, Margaret, Duchess of Norfolk, who lived until 1399. However, when Elizabeth Segrave's father, John de Segrave, 4th Baron Segrave, died on 1 April 1353, Edward III allowed Mowbray to receive a small portion of his wife's eventual inheritance. Estate accounts for 1367 indicate that Mowbray enjoyed an annual income of almost £800 at that time.