He was commissioned, after his father had given William III some encouragement, as colonel of Lord Lorne's Regiment of Foot, a regiment entirely raised by the Argyll family, on 7 April 1694. Campbell served briefly on the continent in the Nine Years' War before the regiment was disbanded in 1698. He also served under the Duke of Marlborough at the Battle of Kaiserwerth in April 1702 during the War of the Spanish Succession. He was appointed a Knight of the Order of the Thistle later that year. Campbell succeeded his father as Duke of Argyll and Chief of Clan Campbell and also became colonel of the 4th Troop of Horse Guards in 1703. For the help he gave the King persuading the Parliament of Scotland to support the Act of Union, he was created Earl of Greenwich and Baron Chatham in 1705. He then returned to the continent and, having been promoted to major-general early in 1706, served as a brigade commander under Marlborough at the Battle of Ramillies in May 1706 and at the Siege of Ostend in June 1706. After being appointed colonel of Prince George of Denmark's Regiment in 1707, he went on to command a brigade at the Battle of Oudenarde in July 1708 and at the Siege of Lille in Autumn 1708. Promoted to lieutenant general in April 1709, he also took part in the Siege of Tournai in June 1709 and the Battle of Malplaquetin September 1709. Appointed a Knight of the Order of the Garter in December 1710, Campbell was promoted to full general and given command of all British forces in Spain at the instigation of the Harley Ministry in January 1711. He replaced James Stanhope who had been forced to surrender at Brihuega the previous December. The Harley government was negotiating an agreement with France which would see Britain recognise Philip V of Spain, in exchange for being allowed to retain Gibraltar and Minorca. After conducting a successful evacuation of the troops from Spain he became Commander-in-Chief, Scotland in 1712. By 1713, however, Campbell had become critical of the ministry, and he joined the Whig opposition in making speeches against the government's policy on the Malt Tax. In July 1714, during Queen Anne's last illness, Campbell gave his full support to the Hanoverian succession. He was rewarded with the colonelcy of the Royal Horse Guards in June 1715.
Jacobite uprising
During the Jacobite Rebellion, Campbell led the government army against the Jacobites led by the Earl of Mar at the Battle of Sheriffmuir in November 1715. The battle was indecisive but favoured the government strategically. He led the advance against the Jacobite capital of Perth, capturing it in December, but was then replaced as commander by William Cadogan.
Later career
He was rewarded by being created Duke of Greenwich in 1719. He went on to become Lord Steward in 1721 and then Master-General of the Ordnance in June 1725 under the Walpole–Townshend Ministry. He also became colonel of the Queen's Regiment of Horse in August 1726 and, having been appointed Governor of Portsmouth in November 1730, he was restored to the colonelcy of the Royal Horse Guards in August 1733. In the 1720s he commissioned the architect James Gibbs to design a Palladian house at Sudbrook Park close to his birthplace at Ham House. Promoted to field marshal on 31 January 1735, Campbell was stripped of his post as Master-General of the Ordnance and the colonelcy of the Royal Horse Guards for opposing the Government of Robert Walpole in 1740. However he was restored to his post as Master-General of the Ordnance in February 1741 and restored to his colonelcy a few days later. Campbell died at Sudbrook Park, Petersham on 4 October 1743 and was buried in Westminster Abbey; his grave is marked by a small lozenge stone to the north east of Henry VII's tomb. A large monument, designed by the French sculptor, Louis-François Roubiliac, was erected for him in the south transept and unveiled in 1749. Argyll Street in London's West End is named after him.
Family
Campbell married first, Mary Brown, daughter of John Brown and Ursula Duncombe, in 1701: they separated soon after the marriage and she died in 1717 and was buried in Westminster Abbey. He married secondly, Jane Warburton, daughter of Thomas Warburton and Anne Williams and maid of honour to Queen Anne, in 1717: Jane died in 1767 and was buried with him in Westminster Abbey. He had four daughters who reached maturity: Caroline Townshend, 1st Baroness Greenwich, Lady Elizabeth Campbell, Lady Anne Campbell and Lady Mary Coke.