John Forbes (July 17, 1714 – March 10, 1796) was the second son of George Forbes, 3rd Earl of Granard in Ireland and Mary Stewart, the eldest daughter of William Stewart, 1st Viscount Mountjoy. He joined the Royal Navy at the age of 12 in 1726 and rose to become Great Britain’s Admiral of the Fleet.

​He first served under his maternal uncle, the Honorable Charles Stewart (who later became Vice-Admiral of the White Squadron.) Forbes sailed to the West Indies 1729 under Stewart’s command and there he was promoted to lieutenant in 1731. As third lieutenant, Forbes served on the Britannia under Admiral Sir John Norris and sailed to Lisbon to support the Portuguese against Spain.

At the experienced age of 23, Forbes was promoted by Norris to commander and appointed him commanding officer of the HMS Poole. He was again promoted to captain in 1737 and commanded a series of battle ships: the HMS Port Mahon, HMS Severn, HMS Tyger, HMS Guernsey, and eventually the 80-gun HMS Norfolk in 1742. As commander of the last, Forbes was engaged in the Battle of Toulon on 11 February 1744 against a combined Franco-Spanish fleet during the War of the Austrian Succession. While the battle was generally disastrous to the British, Forbes was noted to have distinguished himself and his crew.

Forbes was promoted to rear-admiral in 1747 and became second in command to Vice-Admiral John Byng in the Mediterranean and took over command of the Mediterranean Squadron in August 1748. He was elected to the Parliament of Ireland, as Member for St Johnstown in 1751. In 1755, Forbes was promoted to vice-admiral and in 1756 he was appointed a Lord Commissioner of the Admiralty on the Board of Admiralty.

Forbes served on the court martial on the Admiral Byng who was charged with failing to relieve a besieged British garrison during the Battle of Minorca at the beginning of the Seven Years' War. Byng was convicted and, as Lord Commissioner of the Admiralty, Forbes refused to sign Byng's death warrant. He believed that the sentence was illegal and attached to the warrant a document explaining his refusal. King George II refused clemency and a squad of Royal Marines executed Byng in 1757.

In 1758, Forbes found time to marry Lady Mary Capell (1722–1782), the daughter of William Capell, 3rd Earl of Essex. The marriage produced twin daughters in January 1761, Katherine and Mary. They each married Earls: William Wellesley-Pole, 3rd Earl of Mornington, for Katherine and John Villiers, 3rd Earl of Clarendon, for Mary.

Forbes went on to serve as a Lord Commissioner of the Admiralty under successive Governments and later served as Member of Parliament for St Johnstown and then as Member of Parliament for Mullingar in the Parliament of Ireland. His final promotion was to Admiral of the Fleet in 1781. He died at his London home at 3 Savile Row on 10 March 1796 and was buried in the Essex family vault in the parish church of St Mary's Watford next to his wife.

Left, bottom: Lady Mary Capell Forbes (1722 - 1782), daughter of William Capell, 3rd Earl of Essex