He was the son of Sir
John de Montagu, 1st Baron Montagu (died in 1390), and
Margaret de Monthermer. His father was the younger brother of
William Montagu, 2nd Earl of Salisbury. His mother was the daughter of
Thomas de Monthermer, 2nd Baron de Monthermer (1301 –
Battle of Sluys, 1340), and Margaret de Brewes and granddaughter, and
heiress, of
Ralph de Monthermer, 1st Baron Monthermer, and
Joan of Acre. As a young man, Montagu distinguished himself in the
war with France, and then went to fight against the pagans in
Prussia, probably on the expedition led by
Henry Bolingbroke (the future
Henry IV of England). Bolingbroke was to entrust his young son and heir, later
Henry V, to the care of the Montagu family, following the death of his wife
Mary de Bohun. After his mother's death, the earl's wife,
Maud, cared for the young boy at
Courtfield, the Montagus' manor house in
Welsh Bicknor, near
Monmouth. He was summoned to parliament in 1391 as
Baron Montagu. Montagu was a favourite of the King during the early years of the reign of
Richard II. He accompanied the King during his expeditions to Ireland in 1394 and 1395 and, as a
privy councillor, was one of the principal advocates of the King's marriage to
Isabella of Valois. During the trips to France associated with the marriage, he met and encouraged
Christine de Pisan, whose son was educated in the Montagu household. Montagu was a prominent
Lollard, and was remonstrated by the king for this. With the death of his mother in 1395, John inherited the
barony of Monthermer and its estates. In 1397, he became
Earl of Salisbury, on the death of his uncle, and inherited
Bisham Manor and other estates. He continued as one of the major aristocratic allies of
King Richard II, helping to secure the fall of the
Duke of Gloucester and the
Earl of Warwick. He persuaded the king to spare the life of
Warwick. He received a portion of the forfeited Warwick estates and, in 1399, was made a
Knight of the Garter. Early in 1399, he went to France on a successful mission to prevent the proposed marriage of
Henry Bolingbroke and a daughter of the
Duke of Berry. In May, he again accompanied Richard II on an expedition to Ireland. When news reached them of that Bolingbroke had returned to England, Montagu was sent to
Wales to raise opposing forces. When these deserted, Montagu advised King Richard to flee to
Bordeaux. Instead, Richard was imprisoned, Henry took the throne and, in October, Montagu was arrested along with many of Richard's former councillors, and held in the
Tower of London. ==Marriage and issue==