Sir Hugh was an important ally of Simon de Montfort

Simon de Montfort, 6th Earl of Leicester

Simon de Montfort, 6th Earl of Leicester, 1st Earl of Chester , sometimes referred to as Simon V de Montfort to distinguish him from other Simon de Montforts, was an Anglo-Norman nobleman. He led the barons' rebellion against King Henry III of England during the Second Barons' War of 1263-4, and...

 during the reign of Henry III

Henry III of England

Henry III was the son and successor of John as King of England, reigning for 56 years from 1216 until his death. His contemporaries knew him as Henry of Winchester. He was the first child king in England since the reign of Æthelred the Unready...

. He served briefly as Justiciar

Justiciar

In medieval England and Ireland the Chief Justiciar was roughly equivalent to a modern Prime Minister as the monarch's chief minister. Similar positions existed on the Continent, particularly in Norman Italy. The term is the English form of the medieval Latin justiciarius or justitiarius In...

of England in 1260 and as Constable of the Tower of London

Tower of London

Her Majesty's Royal Palace and Fortress, more commonly known as the Tower of London, is a historic castle on the north bank of the River Thames in central London, England. It lies within the London Borough of Tower Hamlets, separated from the eastern edge of the City of London by the open space...

.

Hugh Le Despenser, chief justiciar of England, first plays an important part in
1258, when he was prominent on the baronial side in the Mad Parliament of
Oxford. In 1260 the barons choose him to succeed Hugh Bigod as Justiciar, and
in 1263 the king was further compelled to put the Tower of London in his hands.

He was the son of Hugh le Despenser I

Hugh le Despenser I

Sir Hugh le Despenser was a wealthy landowner in the East Midlands of England, and served as High Sheriff of Berkshire.He was probably the son of a Thomas Despencer, and brother to both Thomas, who died before October 1218, and Rohaise, who married Stephen de Segrave. It is said that he married a...

 and was summoned to Parliament by Simon de Montfort.
Hugh was summoned as Lord Despencer Dec. 14, 1264 and was Chief Justiciar of England and a leader of the baronial party, and so might be deemed a baron

Baron

Baron is a title of nobility. The word baron comes from Old French baron, itself from Old High German and Latin baro meaning " man, warrior"; it merged with cognate Old English beorn meaning "nobleman"...

, though the legality of that assembly is doubtful. He remained allied with Montfort to the end, and was present at the Battle of Lewes

Battle of Lewes

The Battle of Lewes was one of two main battles of the conflict known as the Second Barons' War. It took place at Lewes in Sussex, on 14 May 1264...

. He was killed fighting on de Montfort's side at the Battle of Evesham

Battle of Evesham

The Battle of Evesham was one of the two main battles of 13th century England's Second Barons' War. It marked the defeat of Simon de Montfort, Earl of Leicester, and the rebellious barons by Prince Edward – later King Edward I – who led the forces of his father, King Henry III...

 in August, 1265. He was slain by Roger Mortimer, 1st Baron Wigmore; this caused a feud to begin between the Despencer and the Mortimer families.

By his wife, Aline Bassett, he was father of Hugh the elder Despenser. She was the daughter of Philip Basset

Philip Basset

Philip Basset was the Justiciar of England.Philip was the son of Alan Basset of High Wycombe in Buckinghamshire and his wife, Alice, the daughter of Stephen Gray. He inherited the manor of Wycombe and served as the Justiciar of England between the two terms served by his son-in-law, Hugh le...

, who had also served as Justiciar.