His mother was Margaret Holland, a daughter of Thomas Holland, 2nd Earl of Kent, the son of Joan "the Fair Maid of Kent", a granddaughter of King Edward I and wife of Edward the Black Prince (eldest brother of John of Gaunt) and mother of King Richard II.

Humphrey of Lancaster, 1st Duke of Gloucester, regent for the young King Henry VI, was unable to control the administration of justice and finance, which led to widespread lawlessness.

At the beginning of the second lieutenantcy of Richard, Duke of York, Gloucester declined the office of Lieutenant-Governor, which was then accepted by Somerset, who drew from it a salary of 600 pounds.

He was appointed Admiral of the Sea to the army commander John Talbot, 1st Earl of Shrewsbury,[3] who from August 1440 besieged Harfleur, which had been in French hands for five months.

The English dug a double ditch rampart with only 1,000 men, while Somerset's squadron prevented a French landing by sea, using archers to pick off the enemy at short range.

With the Duke of Gloucester's wife Eleanor charged with treason, Somerset took the opportunity in April 1443 to declare himself Lieutenant of Aquitaine and Captain-General of Guyenne.

[7] His death in 1444,[8] possibly by suicide, and that of his uncle the Cardinal, marked the end of Beaufort influence and left the door open for William de la Pole, 1st Duke of Suffolk, to dominate the government.

By his wife he had an only daughter and sole heiress: As he died without male issue his dukedom went extinct but his earldom passed to his younger brother Edmund Beaufort, 2nd Duke of Somerset (1406–1455).