In April 1372, custody of both Thomas and his elder brother, John, was granted to Blanche Wake, a sister of their grandmother, Joan of Lancaster. On 10 February 1383, he succeeded his elder brother, John Mowbray, 1st Earl of Nottingham, as Baron Mowbray and Baron Segrave, and was created Earl of Nottingham on 12 February 1383. On 30 June 1385 he was created Earl Marshal for life, and on 12 January 1386 he was granted the office in tail male. He fought against the Scots and then against the French. He was appointed Warden of the East March towards Scotland in 1389, a position he held until his death. He was one of the Lords Appellant to King Richard II who deposed some of the King's court favourites in 1387. His party routed the royal favourite Robert de Vere, at the Battle of Radcot Bridge, and Richard was at their mercy. Owing partly to Mowbray's moderate counsels the suggestion to depose him was not carried out, but in the Merciless Parliament of 1388 the king's favourites were tried for treason and were sentenced to death. The king regained his power in 1389 and Mowbray worked his way back into his good graces. Richard detached Mowbray from his colleagues and made him warden of the Eastern March; later he became captain of Calais and the royal lieutenant in the north-east of France. The king took him to Ireland in 1394 and soon afterwards sent him to arrange a peace with France and his marriage with Isabella, daughter of Charles VI. Mowbray was likely instrumental in the murder, in 1397, of the king's uncle, Thomas of Woodstock, 1st Duke of Gloucester, who was imprisoned at Calais, where Nottingham was Captain. In gratitude, on 29 September 1397, the king created him Duke of Norfolk, granting him Arundel's lands in Surrey and Sussex. In 1398, Norfolk quarrelled with Henry of Bolingbroke, 1st Duke of Hereford, apparently due to mutual suspicions stemming from their roles in the conspiracy against the Duke of Gloucester. Before a duel between them could take place, Richard II banished them both. Mowbray left England on 19 October 1398, and was deprived of his offices, but not of his titles. While in exile, he succeeded as Earl of Norfolk when his maternal grandmother, Margaret of Brotherton, Duchess of Norfolk, died on 24 March 1399. He died of the plague at Venice on 22 September 1399. Bolingbroke returned to England in 1399 and usurped the crown on 30 September 1399; shortly afterward, on 6 October 1399, the creation of Mowbray as Duke of Norfolk was annulled by Parliament, although Mowbray's heir retained his other titles.
Arms of Mowbray
The traditional, and historic arms for the Mowbray family are "Gules, a lion rampant argent". Although it is certain that these arms are differenced by various devices, this primary blazon applies to all the family arms, including their peerages at Norfolk. They are never indicated to bear the arms of Thomas Brotherton, nor any other English Royal Arms. Sir Bernard Burkes, C.B., LL.D., Ulster King of Arms, in his book 'A General Armory of England, Scotland, Wales, and Ireland', 1884, page 713, provides the following detailed listing of the Mowbray/Norfolk arms: "Mowbray. Gu. a lion ramp. ar. Crest—A leopard or, ducally gorged ar.; granted by patent to the first duke, 17 Richard II. , which acknowledges his right to bear for his crest "a golden leopard with a white label," the crest of his maternal ancestor, Thomas Plantagenet, of Brotherton, Earl of Norfolk, and grants the coronet instead of the label, which right belong to the King's son.
Mowbray's quarrel with Bolingbroke and subsequent banishment are depicted in the opening scene of Shakespeare's Richard II. Thomas Mowbray prophetically replies to King Richard's "Lions make leopards tame" with the retort, "Yea, but not change his spots." Mowbray's death in exile is announced later in the play by the Bishop of Carlisle.
