In 1754, he was made commander of the sloop Jamaica and served in her on the North American station. In July 1756, while still on the North American station, he took command of the sloop HMS Lively.

At the outbreak of the Seven Years War in 1756, the navy was rapidly expanded which benefited Hood. Later that year Hood was promoted to Post Captain and given command of HMS Grafton. In 1757, while in temporary command of Antelope (50 guns), he drove a French ship ashore in Audierne Bay, and captured two privateers. His zeal attracted the favourable notice of the Admiralty and he was appointed to a ship of his own.

In 1759, when captain of the Vestal (32), he captured the French Bellone (32) after a sharp action. During the war, his services were wholly in the Channel, and he was engaged under Rodney in 1759 in the Raid on Le Havre, destroying the vessels collected by the French to serve as transports in the proposed invasion of Britain.

He was appointed in Commander-in-Chief, North American Station in July 1767. He returned to England in October 1770.

In 1778, he accepted a command which in the ordinary course would have terminated his active career, becoming Commissioner of the dockyard at Portsmouth and governor of the Naval Academy. These posts were generally given to officers who were retiring from the sea.

In 1778, on the occasion of the King's visit to Portsmouth, Hood was made a baronet.

The war was deeply unpopular with much of the British public and navy. Many admirals had declined to serve under Lord Sandwich, the First Lord of the Admiralty. Admiral Rodney, who then commanded in the West Indies, had complained of a lack of proper support from his subordinates, whom he accused of disaffection. The Admiralty, anxious to secure the services of trustworthy flag officers, promoted Hood to rear admiral on 26 September 1780, and sent him to the West Indies to act as second in command under Rodney, who knew him personally. He joined Rodney in January 1781 in his flagship Barfleur, and remained in the West Indies or on the coast of North America until the close of the War of American Independence. The expectation that he would work harmoniously with Rodney was not entirely justified. Their correspondence shows that they were not on friendly terms; but Hood always did his duty, and he was so able that no question of removing him from the station ever arose. The unfortunate turn for the British taken by the campaign of 1781 was largely due to Rodney's neglect of Hood's advice. If he had been allowed to choose his own position, he could have prevented the Comte De Grasse from reaching Fort Royal with the reinforcements from France in April.

When Rodney decided to return to Britain for the sake of his health in the autumn of 1781, Hood was ordered to take the bulk of the fleet to the North American coast during the hurricane months. Hood joined Admiral Thomas Graves in the unsuccessful effort to relieve the army at Yorktown, when the British fleet was driven off by the French Admiral, the Comte de Grasse, at the Battle of the Chesapeake.

When he returned to the West Indies, he was for a time in independent command owing to Rodney's absence in England. De Grasse attacked the British islands of St Kitts and Nevis with a force much superior to Hood's squadron. Hood made an unsuccessful attempt in January 1782 to save them from capture, with 22 ships to 29, and the series of bold movements by which he first turned the French out of their anchorage at Basseterre of St Kitts and then beat off their attacks, were one of the best accomplishments of any British admiral during the war.

In 1782 Hood took part in a British fleet under Rodney which defeated a combined French and Spanish fleet which was planning an invasion of Jamaica. The French commander De Grasse, who had been responsible for the victory at Chesapeake was captured and taken back to Britain as a prisoner. Hood was deeply critical of Rodney for not pushing home his victory against the retreating enemy fleet. Had they pursued, he suggested, the British might have taken additional prizes and destroyed the French naval presence in the Caribbean. Eventually Hood was ordered to chase and with his division of 12 ships he captured 4 ships at the Mona Passage on April 19 thus completing the defeat.

While serving in the Caribbean Hood became acquainted with, and later became a mentor to Horatio Nelson who was a young frigate commander. Hood had been a friend of Nelson's uncle Maurice Suckling. In 1782 Hood introduced Nelson to the future King William, Duke of Clarence who was then a serving naval officer in New York.

Hood was made an Irish peer for his role in the victory at the Battle of the Saintes on 9 April and 12 April near Dominica.

During the peace, he entered the British Parliament as Member for Westminster in the election of 1784 where he was a supporter of the government of William Pitt the Younger. In 1786 he became Commander-in-Chief, Portsmouth, holding that post until 1789. He was promoted to vice admiral in 1787, and in July 1788, was appointed to the Board of Admiralty under the Second Earl of Chatham, brother of the Prime Minister.

On the outbreak of the French Revolutionary War in 1793, he was sent to the Mediterranean Sea as Commander-in-Chief. His period of command, which lasted from May 1793 to October 1794, was very busy. In August 1793 French royalists and other opponents of the revolution took over the town and invited Hood, whose fleet was blockading the city, to occupy the town. Hood, without time to request for instructions from the Admiralty in London, moved swiftly to take command of the port. There were two main reasons for the British move. It was hoped that Toulon could be a centre of French resistance to Paris, and also to take possession of the French Mediterranean fleet of fifty eight warships, which lay in the harbour. It was hoped that depriving the French revolutionaries of their maritime resources would cripple the revolution. He occupied Toulon on the invitation of the French royalists, in co-operation with the Spaniards and Sardinians. In December of the same year, the allies, who did not work harmoniously together, were driven out, mainly by the generalship of Napoleon. Hood ordered the French fleet burned to prevent them falling back into the hands of the revolutionaries, a task carried out by Captain Sidney Smith. Afterwards, Hood and his British force withdrew to maintain their blockade of the coast, while the French republicans reoccupied the city.

Hood then turned to the occupation of Corsica, which he had been invited to take in the name of the King of Britain by Paoli. The island was for a short time added to the dominions of George III, chiefly by the exertions of the fleet and the co-operation of Pascal Paoli, who ruled the Kingdom of Corsica. While the occupation of Corsica was being effected, the French at Toulon had so far recovered that they were able to send a fleet to sea. In June, Hood sailed in the hope of bringing it to action. The plan which he laid to attack it in the Golfe Jouan in June may possibly have served to some extent as an inspiration, if not as a model, to Nelson (who has been recorded as saying that Hood was "the greatest sea officer I ever knew.") for the Battle of the Nile, but the wind was unfavourable, and the attack could not be carried out. In October, he was recalled to England in consequence of some misunderstanding with the admiralty or the ministry, which has never been explained.

Samuel Hood was created Baron Hood of Catherington in 1778 by King George III, an Irish Baron in 1782 and Viscount Hood of Whitley, Warwickshire in 1796 with a pension of £2000 per year for life (about £300,000 a year in present (2010) terms). He became Commander - in - Chief, Portsmouth again in June 1792. In February 1793 he became Commander - in - Chief, Mediterranean Fleet. In 1796, he was named Governor of the Royal Naval Hospital at Greenwich in London, a position which he held until his death in 1816. He was elected as Tory Member of Parliament for Westminster from 1784 to 1788 and from 1790 to 1796 as Member for Reigate, serving with his younger brother Alexander under Pitt the Younger. He lived long enough to see Britain triumph in the Napoleonic Wars and was chief mourner at Nelson's funeral. A peerage of Great Britain was conferred on his wife, Susannah, as Baroness Hood of Catherington in 1795. Samuel Hood's titles descended to his youngest son, Henry (1753 – 1836), the ancestor of the present Viscount Hood. Lord Samuel Hood and his wife had two other sons Samuel and Thomas. Samuel died in infancy , and many sources suggest that Thomas also died similarly, but it is now known that Thomas survived until 1800 or so.

There are several portraits of Lord Hood by Abbot in the Guildhall and in the National Portrait Gallery. He was also painted by Joshua Reynolds and Thomas Gainsborough.

A biographical notice of Hood by McArthur, his secretary during the Mediterranean command, appeared in the Naval Chronicle. His correspondence during his command in America was published by the Navy Record Society. The history of his campaigns will be found in the historians of the wars in which he served: for the earlier years, Beatson's Naval and Military Memoirs; for the later, James's Naval History, vol. i., for the English side, and for the French, Troudes, Batailles navales de la France, ii. and iii., and Chevalier's Histoire de la marine française pendant Ia guerre de l'indépendance américaine and Pendant Ia République.

In 1792, Lieutenant William Broughton, sailing with the expedition of George Vancouver to the Northwest Coast of North America, named Mount Hood in present day Oregon, and Hood's Canal in present day Washington, after Hood. Two US Naval ships were named after Mount Hood, which could be considered mildly ironic as Hood had served against the United States during the American War of Independence. Two of the three ships of the Royal Navy named HMS Hood were named after him as well, including HMS Hood (51), sunk by the Bismarck in 1941 during World War II.