Molesworth, Richard (1680–1758), 3rd Viscount Molesworth , field-marshal, MP, and commander-in-chief in Ireland, was second son of Robert, 1st Viscount Molesworth (qv), of Swords, Co. Dublin, and Philipstown, King's Co., and his wife Letitia, third daughter of Richard Coote, Lord Colooney. Educated privately, he was admitted to the Middle Temple in London in August 1700 to begin studies for the bar. When the war of the Spanish succession began in 1701 he abandoned his legal studies and volunteered to serve with the army in Flanders. Through the influence of the earl of Orkney, his father's friend, he was commissioned into the Royal Scots in April 1702 and commanded a company of the regiment at the battle of Blenheim (August 1704). Appointed as an ADC to the duke of Marlborough (qv), he saved the duke's life at the battle of Ramillies (23 May 1706), giving him his mount after he had been unhorsed in a cavalry charge. Promoted to captain and lieutenant-colonel in the Coldstream Guards in May 1707, he served in the relief of Brussels (1708) and at the siege of Mons (1709), where he was blown into the air by a mine but escaped serious injury.
In June 1710 he succeeded to the command of Col. Moore's regiment of foot and campaigned in Catalonia under the command of the duke of Argyll. He was in garrison with his regiment in Port Mahon, Minorca, when the peace of Utrecht was signed in 1713, and the regiment was disbanded. Appointed lieutenant of the ordnance in Ireland in December 1714, he became MP for Swords, Co. Dublin (1714–26). After the outbreak of the Jacobite rebellion of 1715, he was given a commission to raise a regiment of dragoons and was wounded at the battle of Preston in November 1715. The regiment was disbanded at the end of the rebellion in 1718 and Molesworth was put on half pay. He became colonel of the 27th Foot (Royal Inniskilling Fusiliers) in March 1725, and succeeded to the family title in 1726 on the death of his brother John, 2nd Viscount Molesworth, British ambassador to Tuscany and Sardinia.
Appointed (1732) colonel of the 9th Dragoons (later the 9th Queen's Royal Lancers), he was promoted to major-general (1735). Sworn of the Irish privy council (October 1733), he was made deputy-keeper of the great seal of Ireland (1736). He succeeded Gen. Wynne as colonel of the 5th Royal Irish Dragoon Guards in June 1737, a colonelcy that he held until his death. Promoted to lieutenant-general on the Irish establishment (1739), he was appointed master-general of the Irish ordnance in July 1740. Further promotions followed, to lieutenant-general on the English establishment (July 1742) and general (1746). In September 1751 he was appointed commander-in-chief in Ireland, which also came with an honorary appointment as governor of the Royal Hospital at Kilmainham. He was promoted to field marshal in November 1757.
Alongside his military career, he eagerly sought ways to improve his family's dwindling finances, which had been ruined by his father's overspending. In 1708 he had been appointed comptroller of customs at Newcastle, which brought a salary of £300 a year; the duties were carried out by a deputy. He invested in the notorious South Sea Company, losing heavily in the ‘South Sea Bubble’ financial crisis of 1720. Interested in the sciences, or perhaps in the £20,000 reward offered by parliament in 1714 for a solution to the longitude problem, he experimented with methods of calculating longitude. He developed his own type of chronometer, which was favourably reviewed by Sir Isaac Newton. In March 1721 he was admitted as a member of the Royal Society. After his promotion to lieutenant-general he published A short course of standing rules for the government of an army, designed for use in the field: with some useful observations drawn from experience. Around 1723, he considered writing a biography of the duke of Marlborough but was refused access to the duke's papers by the duchess, who denied that Molesworth had saved the duke's life at Ramillies.
He died 12 October 1758 in London and was buried in Kensington. The celebrated Florentine medallist Antonio Selvi cast a commemorative medal of him, supposedly in recognition of his actions at Ramillies in 1706. This medal, showing Molesworth dressed as a Roman warrior, is in the British Museum. There is a large collection of his papers in the NLI, in the Molesworth and Clements collections.
He married first Jane (d. April 1742), daughter of a Mr Lucas of Dublin; they had one son, who died in infancy, and three daughters. He married secondly (February 1743) Mary, daughter of William Usher, archdeacon of Clonfert, and Mary (‘Jenny’) Usher. They had one son, Richard Nassau Molesworth (1748–93), who succeeded as 4th viscount, and six daughters. Lady Molesworth was granted a pension of £500 a year on the death of her husband. On the night of 6–7 May 1763 her house at Upper Brook St., London, caught fire and, showing great courage and presence of mind, she broke windows and threw out mattresses into the street, allowing her eldest daughter, Henrietta, to jump to safety. Overcome by smoke, she died in the flames along with her brother, Capt. Usher, RN, two younger daughters, Melosina and Mary, their governess, and four other servants. George III was so upset by this tragedy that he ordered a pension of £390 a year be held in trust for the surviving daughters.