Born at Hamilton in Lanarkshire on 19 June 1606, James was the eldest son of the 2nd Marquis of Hamilton, also named James, and of Lady Anne Cunningham, daughter of the Earl of Glencairn. The Hamilton family was among the most powerful in Scotland, having next claim to the Scottish throne after the Stewarts. From 1609 James was styled the Earl of Arran and was brought up under the influence of his devout Calvinist mother until 1620, when he was summoned by his father to London and introduced at the court of King James I. Arran was married at the age of 16 to Mary Feilding, daughter of the Earl of Denbigh and niece of the Marquis (later Duke) of Buckingham. The marriage was arranged by Buckingham to advance the interests of his relatives — the Feildings were a relatively obscure Warwickshire family, while Arran was heir to the leading noble family of Scotland. Although he was eventually reconciled with Mary, Arran resented his lowly marriage for the rest of his life.
In 1623, Arran was among the noblemen who accompanied Prince Charles and Buckingham to Madrid in the unsuccessful attempt to negotiate a marriage between Charles and the Spanish Infanta. Arran struck up a close friendship with Charles on the journey and was made a Gentleman of the Bedchamber on their return to England. When his father died in 1625, he inherited the titles of 3rd Marquis of Hamilton and 2nd Earl of Cambridge. After Buckingham's assassination in 1628, King Charles I appointed Hamilton to Buckingham's old post of Master of the Horse, which made him one of the King's closest attendants.
In 1631, Hamilton led a volunteer force of 6,000 English and Scottish troops to fight for Gustavus Adolphus against the Catholic Hapsburgs in Germany. Most of his army died from sickness before taking part in any fighting. Hamilton tried to persuade King Charles to commit more British troops to the European wars, but Charles would not be drawn and ordered Hamilton's return to Britain in September 1632. However, Hamilton kept up his association with the Protestants in Europe. He acted as an unofficial representative at the British court for the interests of both Gustavus Adolphus of Sweden and the exiled Palatinate family.
Hamilton was appointed to the Privy Council in March 1633. As one of the nobles closest to the King, he became the chief adviser in Scottish secular affairs, though he had no influence on matters of religion. He was active in a number of lucrative commercial enterprises, and became a noted collector of Italian and Venetian art.
During the crisis brought about by the signing of the Scottish National Covenant, Hamilton was appointed King's Commissioner in Scotland to negotiate with the Covenanters. He tried unsuccessfully to persuade King Charles to relax his uncompromising stance during the summer of 1638, then represented the King at the Glasgow Assembly in November. Realising that the Assembly unanimously favoured the Covenanters, Hamilton declared it illegal and announced its dissolution. His order was ignored and the Assembly continued to sit in defiance of Hamilton and the King's authority, leading to armed confrontation between England and Scotland.
During the First Bishops' War (1639), Hamilton was appointed commander of the King's forces in Scotland and led a naval campaign in an ineffective attempt to land English troops behind Scottish lines. His mother, Lady Anne Cunningham, led her own troop of horse to Leith in support of the Covenanters and is said to have declared that she would personally shoot her son if the English troops landed. Hamilton joined the King at Berwick for the treaty negotiations. He resigned as King's Commissioner in July 1639, with the intention of ingratiating himself with the Covenanters in order to inform the King of their plans. Hamilton kept a low profile during the Second Bishops' War, regarding the policies of the Earl of Strafford as dangerous to the King and to Scotland. He supported Strafford's impeachment in 1641.
In August 1641, Hamilton accompanied Charles on his last visit to Scotland. He attempted to form an alliance between the King and the covenanting Earl (later Marquis) of Argyll. This earned the enmity of the Royalist Marquis of Montrose who mistrusted Argyll. Hamilton and Argyll were forced to flee from Edinburgh in October 1641 on the discovery of a muddled plot against them perpetrated by hot-headed Royalists (the "Incident"). However, a temporary understanding between the King and the Covenanters was reached. Accompanied by Hamilton, the King returned to England in November 1641 believing that the Covenanters fully supported him against the English Parliament.
Hamilton was sent back to Scotland in July 1642 and worked to prevent the intervention of the Scots in the impending civil war. This soon caused a breach with Argyll and further hostility from Montrose, who proposed immediate military action against the Covenanters. The King favoured Hamilton's intrigues over Montrose's policy of direct action, creating him Duke of Hamilton in April 1643. However, Hamilton was unable to prevent or even hinder the assembly of an informal Scottish parliament — the Convention of Estates — which met in June 1643 without the King's authority and began to form links with the Westminster Parliament. Hamilton and his brother, the Earl of Lanark, were forced to leave Scotland after they refused to take the Covenant. They arrived at the King's headquarters at Oxford on 16 December 1643. In disgrace for having failed to keep Scotland loyal to the King, Hamilton was stripped of his offices and imprisoned at Pendennis Castle in Cornwall. In 1645, he was moved to St Michael's Mount, and languished there until he was liberated by Fairfax's victorious troops on 23 April 1646.
Hamilton made his way to Newcastle where King Charles was in the hands of the Scottish army and, after some awkwardness, was accepted back into the King's favour. He joined the many voices urging Charles to accept the Newcastle Propositions as a basis for a treaty with Parliament but was persuaded to remain in Charles' service even after the Propositions had been rejected.
Hamilton's renewed involvement in Scottish affairs caused a split between his own supporters and the hardline Covenanters led by Argyll, particularly over the terms of the Engagement that the King signed with the Scottish Commissioners in December 1647. Hamilton took command of the Engager army that invaded England in the hope of collaborating with English Royalists in July 1648. His forces were held in check by Major-General Lambert until Cromwell marched up from Wales and decisively defeated him at the battle of Preston. Although he mismanaged the battle, Hamilton courageously led a body of horse to support Sir Marmaduke Langdale as he attempted to hold off Cromwell's advance.
A few days after his defeat, Hamilton was taken prisoner at Uttoxeter. The House of Lords voted to liberate him on payment of a fine of £100,000 but after Pride's Purge in December 1648, the vote was repealed and he was imprisoned at Windsor Castle. Cromwell himself interviewed Hamilton, offering to spare his life if he would give information to convict the Englishmen who had collaborated in the Engager invasion, but Hamilton refused to betray his associates. Along with four English Royalists, he was brought to trial before the High Court of Justice in February 1649 as the Earl of Cambridge. His title in the English peerage made him technically an Englishman and subject to the High Court's jurisdiction. He was found guilty of treason and beheaded at Westminster on 9 March 1649.
References:
John J. Scally, James, first duke of Hamilton, Oxford DNB, 2004
David Stevenson, The Scottish Revolution 1637-44, 1973
David Stevenson, Revolution & Counter-Revolution in Scotland 1644-51, 1977
C.V. Wedgwood, The King's Peace, 1955