Eldest son of the 2nd Earl of Essex, who was executed for treason by Queen Elizabeth in 1601. On the succession of King James I to the throne of England in 1604, Devereux was restored to his father's estate. In 1606, the King arranged a marriage between Essex and Frances Howard, daughter of the Earl of Suffolk. Since Essex was only fourteen at the time of his marriage, he was sent abroad until he came of age. Meanwhile, Frances became involved with Sir Robert Carr and rejected Essex when he returned to England. The marriage ended in a humiliating divorce in 1613 on the grounds of Essex's impotence.
From 1620-4, Essex served in Protestant armies in Germany and the Low Countries. He joined Sir Horace Vere's expedition to defend the Palatinate in 1620 and served with Prince Maurice of Nassau from 1621. In 1624, he commanded a regiment in the unsuccessful campaign to relieve the siege of Breda. The following year, Essex was appointed Vice-Admiral in Sir Edward Cecil's expedition against Cádiz, which ended in disaster for the English. But although Essex's military career during the 1620s was undistinguished, he earned the affection and loyalty of the troops who served under him because of his willingness to share the same hardships.
Essex alternated his military service with his political duties in the House of Lords. Easily offended and acutely sensitive to the honour of his family name, Essex became estranged from Court life and was associated with the Parliamentary opposition to King James and his successor King Charles I. Because of his criticism of the Duke of Buckingham after Cádiz, Essex was denied command of an expeditionary force sent to Denmark; he then declined an offer to command a regiment on the expedition to La Rochelle in 1627. Essex refused to pay the forced loans demanded by the King in 1626-7, and he supported the Petition of Right in 1628. After the dissolution of the 1628-9 Parliament, he withdrew into private life at his estates at Chartley in Staffordshire.
In 1630, Essex married Elizabeth Paulet, but six years later this marriage collapsed because of her adultery with Sir Thomas Uvedale. When Elizabeth gave birth to a son in November 1636, many believed Uvedale to be the father. Essex once again became the laughing-stock of the Court. He accepted the child as his own and even forgave the Countess, but when the child died the following month Essex despairingly gave up all hope of a successful marriage and an heir to his title.
In 1639, King Charles' uncompromising religious policy led to the Bishops' Wars between England and Scotland. Essex had more military experience than anyone of similar rank in the aristocracy and was appointed second-in-command to the Earl of Arundel, the Earl-Marshal of England, in the army sent against the Scots. However, at the request of Queen Henrietta Maria, Essex was suddenly demoted to Lieutenant-General of Horse in favour of the Queen's courtier the Earl of Holland. When Scottish leaders approached Essex to use his influence to halt the march on Scotland, the King's mistrust of him deepened — even though he had dutifully handed over their letters unopened.
During the Short Parliament, Essex was one of the minority of 25 peers in the House of Lords who voted against granting money to continue the war against Scotland unless Parliament's grievances were first addressed. He was not offered any command in the Second Bishops' War (1640) but was one of the commissioners appointed to negotiate a treaty with the Covenanters. When the Long Parliament met in November 1640, Essex emerged as the leading opposition peer in the House of Lords. He cooperated with John Pym, leader of the House of Commons, in the prosecution of the Earl of Strafford and in the dismantling of the Court of Star Chamber and other institutions that had enabled the King to rule without Parliament.
King Charles made belated attempts to win Essex's support during 1641. In February, Essex was one of seven opposition Lords appointed to the King's Privy Council. In July, he was appointed Lord Chamberlain and given command of all armed forces south of the River Trent while the King made a state visit to Scotland. However, King Charles never fully trusted Essex nor took him into his confidence, which increased his sense of wounded honour. Meanwhile Parliament looked to Essex as a potential leader in its plans to reorganise the armed forces.
In January 1642, Essex was told by the Countess of Carlisle, from gossip at Court, that the King intended to seize the Five Members regarded as his leading opponents in the House of Commons. Essex warned the MPs, who went into hiding. After the failure of his attempt to arrest them, the King was forced to make a humiliating withdrawal from London. Essex refused the King's command to join him at York and was dismissed from his office of Lord Chamberlain. He was the first member of the House of Lords to accept Parliament's Militia Ordinance in March 1642.
As the highest-ranking nobleman to support Parliament, Essex was appointed to the Committee of Safety in July 1642 and made Captain-General of the Parliamentarian armies on the outbreak of civil war. Essex proved meticulous in planning his campaigns but was always cautious in carrying them out. He believed that the outcome of the war should be decided by negotiation with the King from a position of strength rather than from an outright military victory over him. Although criticised for his lack of flair and initiative, "Old Robin" remained popular with his troops.
He commanded at Edgehill, the first pitched battle of the English Civil War, where he stood alongside his men wielding a pike at the head of an infantry regiment. Essex stood his ground in the defence of London later that year, though his refusal to pursue and attack the Royalist army as it withdrew from London disappointed many Parliamentarians. In 1643, Essex besieged and captured Reading, but he was unable to carry home the threat to the King's headquarters at Oxford. Criticism of Essex's generalship began to be heard. Members of the Parliamentary "War Party" praised his military rival Sir William Waller and hinted that Essex was reluctant to inflict a total military defeat on the King. However, Essex fought his most brilliant campaign when he successfully relieved the siege of Gloucester and fought his way back to London at the first battle of Newbury in September 1643. Essex's Gloucester campaign halted a long run of Royalist successes and revived flagging morale in London.
After John Pym's death at the end of 1643, Sir Henry Vane emerged as political leader in Parliament. Vane had no confidence in Essex's abilities as a general and manoeuvred to have him removed from command. Essex opposed the formation of the Committee for Both Kingdoms in February 1644 because he realised that it threatened his authority. His political influence was further undermined by the failure of his military campaigning that year when, after arguing with Waller, he disobeyed orders from Parliament, split his forces and marched into the West. Although he relieved the siege of Lyme, his subsequent invasion of Cornwall resulted in the disastrous loss of his army at Lostwithiel in September 1644. This proved to be Essex's last military campaign. He supported the Earl of Manchester against Oliver Cromwell's criticisms of Manchester's leadership of the Eastern Association, and in December 1644 joined an unsuccessful attempt to have Cromwell impeached for sedition. Essex led the opposition in the House of Lords to the measures proposed in the Commons for the reorganisation of Parliament's army, but he was finally obliged to resign his commission, which he did with a dignified speech on 2 April 1645, the day before the Self-Denying Ordinance was passed.
Essex lived in semi-retirement, a revered and respected figure once he had laid down his military commissions. He suffered a stroke after stag hunting at Windsor and died on 14 September 1646. He was buried in Westminster Abbey with great pomp and ceremony. A month after the funeral, his grave was vandalised and his effigy beheaded by a former Royalist soldier. The effigy was refurbished but was finally destroyed on the orders of Charles II after the Restoration, though Essex's body was left undisturbed. He died without male heirs, so the Essex title was extinguished.
References:
A.H. Burne & P. Young, The Great Civil War, 1959
S.R. Gardiner, Robert Devereux, third Earl of Essex, DNB, 1888
John Morrill, Robert Devereux, third earl of Essex, Oxford DNB, 2004