The eldest son of Henry Somerset, fifth Earl and first Marquis of Worcester, Edward Somerset was brought up as a Roman Catholic at Raglan Castle, his family seat in Monmouthshire. He was styled Lord Herbert when his father inherited the earldom of Worcester in 1628. Herbert's first marriage was to Elizabeth Dormer; they had two daughters and one son, Henry Somerset, later the first Duke of Beaufort, before Elizabeth's death in 1635. His second marriage (1639) was to Margaret O'Brien, daughter of the Earl of Thomond, which brought important connections with fellow Catholics in the Irish nobility. Although he held public office as deputy lieutenant of Monmouthshire, Lord Herbert's principal interest was scientific experiment. He employed Caspar Calthoff, a Dutch engineer, to assist him with mechanical experiments at Raglan which included a hydraulic system to raise water for irrigation.
On the outbreak of the First Civil War in 1642, Herbert's father the Earl of Worcester became a major financial contributor to the Royalist war-effort, for which he was created Marquis of Worcester in March 1643. Lord Herbert acted as an agent between his father and the King. He was commissioned lieutenant-general of Royalist forces in south Wales but his relations with the Royalist commander, the Marquis of Hertford, were strained. Early in 1643, Herbert mustered a force of 1,500 foot and 500 horse to besiege the Parliamentarian stronghold of Gloucester. On 24 March, Sir William Waller surprised the Royalist encampment at Highnam and captured or killed most of the army. Herbert, who was not present, laid the blame for the disaster on others. He was subsequently appointed lieutenant-general of the associated counties of Hereford, Monmouth, Glamorgan, Brecknock and Radnor but met with little military success.
As he was a Catholic with connections to the Irish nobility, Herbert was commissioned by King Charles to negotiate a secret treaty with the Confederates to raise an Irish army to fight against Parliament. The King created him Earl of Glamorgan and promised him a dukedom and the marriage of his eldest son to the Princess Elizabeth if the mission succeeded. Negotiations for the so-called Glamorgan Treaty continued throughout 1645 but caused political damage to the Royalist cause because of the concessions promised to Irish Catholics. The Marquis of Ormond publicly disassociated himself from Glamorgan and denounced him as a traitor; the King finally disavowed him early in 1646.
Glamorgan contemplated abandoning the King's cause and entering the French service but the papal nuncio Archbishop Rinuccini persuaded him to remain in Ireland where he was appointed to the Confederate Supreme Council under Rinuccini's presidency. He supported Rinuccini's denunciation of the First Ormond Peace in August 1646 and the Archbishop appointed him commander of Confederate forces in Munster. However, the soldiers rejected Glamorgan's authority and declared for their former commander Viscount Muskerry.
Although Glamorgan succeeded as the second Marquis of Worcester on the death of his father in December 1646, his family estates were sequestered by order of Parliament. He left Ireland for France in March 1648. When he returned to England in July 1652 he was placed under arrest and held in the Tower of London until October 1654 when he was released on bail, probably through the intervention of the Protector Oliver Cromwell, who was the main beneficiary of the confiscation of his estates. Worcester was granted a small pension in 1655 and resumed his collaboration with the engineer Caspar Calthoff. The Protectorate government took an interest in their work and set aside an area of Vauxhall, south of London, for mechanical and scientific experimentation. Their "water commanding engine" may have been an early precursor of the steam engine.
Worcester recovered his estates after the Restoration but he remained heavily in debt and was disappointed to receive no reward for his family's service to the Royalist cause during the civil wars. His claim to the dukedom of Somerset was not acknowledged neither was the earldom of Glamorgan formally recognised so did not descend to his heirs. After his death in 1667, the marquisate of Worcester passed to his son Henry.
Sources:
S.R. Gardiner, History of the Great Civil War vol. iii (London 1889)
A.F. Pollard, Edward Somerset, sixth earl and second marquess of Worcester and titular Earl of Glamorgan, DNB 1897
Stephen K. Roberts, Edward Somerset, second marquess of Worcester, Oxford DNB, 2004