Clinton was born in Newfoundland, then a British colony over which his father, George Clinton, was governor. The younger Clinton grew up mostly in New York, where his father was Royal Governor from 1741 (although it was 1743 before he actually got there) until 1753. When he was old enough, Henry Clinton spent a time in the New York militia.
In 1751, the young Henry went to England and began his career in the British Army rising in rank with commissions purchased by his family. He was at first commissioned as a Captain in the Coldstream Guards, and by 1758 had risen to be a Lieutenant-Colonel in the Grenadier Guards. Late during the Seven Years' War, Clinton distinguished himself (1760–1762) as an aide-de-camp to Duke Ferdinand of Brunswick, and he was promoted to full Colonel in 1762. After the peace, he received the command of a regiment of foot. Clinton was promoted to Major-General in 1772, in which same year he obtained a seat in Parliament through the influence of his cousin Henry Pelham-Clinton, the Duke of Newcastle. He remained a Member of Parliament until 1784, first for Boroughbridge and subsequently for Newark-on-Trent.
In March 1775, in response to the American Revolutionary War, King George III dispatched reinforcements there under Clinton and fellow Major-Generals William Howe and John Burgoyne, to strengthen the British position in Boston. On 17 June, with the British army having been besieged in Boston since April, Clinton was one of the British field commanders in the Battle of Bunker Hill. This assault to drive the rebels from the heights north of Boston harbor was successful, but only at the heavy cost of over 1,000 British casualties. Fearing that a similar situation would arise to the south of the harbour, upon Dorchester Heights, Clinton strongly advocated that British forces secure them against rebel occupation, but his warnings went unheeded by Howe. In January 1776, Clinton was sent south with a small fleet and 1,500 men, to assess military opportunities in the Carolinas. During his absence, in March, his fears were realized when the Dorchester Heights were occupied and fortified by the rebels, causing the British to retreat to Halifax, Nova Scotia.
In June, an attack under Clinton's command was made on Fort Sullivan at Charleston, South Carolina. It was a humiliating failure, and his campaign in the Carolinas was called off. The attack, made with the co-operation of the Royal Navy failed because Clinton badly under-estimated the strength of the American forces in Charleston. The naval commander, Sir Peter Parker engaged in an abortive attack on Fort Moultrie on Sullivan's Island, which, being far more heavily fortified than anticipated, badly damaged the British squadron. Also present at the battle was Charles Cornwallis and Horatio Nelson.
Clinton and his twenty-five ships rejoined the main fleet to participate in General Howe's August 1776 assault on New York City. Clinton presented arguments for launching the attack up the Hudson River, but these were dismissed by General Howe. After the British had established themselves at Gravesend on Long Island, Clinton's new plan of campaign was followed and proved a great tactical success in the Battle of Long Island, for which he was made a Lieutenant-General awarded the Order of the Bath.
In December, Howe sent Clinton, in command of 6,000 men, to occupy Newport, Rhode Island, which he soon accomplished.
In May of 1778, after the British disaster of the Saratoga Campaign, Clinton replaced Howe as Commander-in-Chief for North America. He assumed command in Philadelphia. France had by this time overtly entered the war on the American side, and because of this Clinton was ordered by his government to send 5,000 of his troops to the Caribbean, which forced him to withdraw from Philadelphia. He conducted a skillful retreat thence to New York. Having thus concentrated his forces, for a time he pursued a policy of making mere forays from there. Before the year's end, though, he regained the initiative for the British by sending an expedition south, to strike at Georgia. This force took Savannah in December, and by early 1779 it had gained control of the hinterland.
This campaign in Georgia presumed strong silent Loyalist support that would appear as soon as the redcoats were present in strength. The notion that the South was more likely to be friendly to British forces had been entertained by the American Secretary, George Germain for much of the war to date, a notion fed by Loyalist exiles in London. While the South on the whole was less receptive to the concept of independence from Britain, who provided the market for most of their plantation goods, the expected wave of public support for the arrival of the British troops never materialised, leaving Clinton and his subordinates isolated. For much of the rest of the war in the South, British commanders almost aimed at mobilising Loyalist support, but the results were never as helpful as they had hoped.
By late in 1779, having called in the troops from Newport to do so, Clinton had assembled a strong force for the next step in this strategy, an invasion of South Carolina. Clinton took personal command of this campaign, and the task force with 14,000 men sailed south from New York at the end of the year. By early 1780, Clinton had brought Charleston under siege. In May, working together with Admiral Mariot Arbuthnot, he forced the surrender of the city, with its garrison of 5,000, in a stunning and serious defeat for the rebel cause. It was during the siege and capture of Charleston that Clinton's inability to co-operate with equal ranking officers started to become more evident. Arbuthnot and Clinton did not work together well, and this feud was to last until the end of the war with disastrous results for the unity of the British high command.
Clinton then returned to New York, leaving 8,000 British troops the southern theatre under the command of General Cornwallis, his second-in-command. From New York, he oversaw the campaign in the South, and his correspondence to Cornwallis through showed an active interest in the affairs of his southern army. However, as the campaign progressed, he grew further and further away from his subordinate. As the campaign drew to a close, the correspondence becomes more and more acrimonious. Part of this may be due to George Germain, whose correspondence with Cornwallis may have convinced the junior officer to start disregarding the orders of his superior and consider himself to be an independent command.
In 1782, Clinton was replaced as Commander-in-Chief by Sir Guy Carleton, and he returned to England. His replacement is linked to the fate of the southern army, which was surrounded and forced to surrender by George Washington and the Comte de Rochambeau, who commanded a combined French-American Army after the Siege of Yorktown.
Sir Henry Clinton held the command in America for four years, ending in disaster and defeat; his name was forever to be linked with the downfall of British control of the colonies. Historians have since shifted more blame onto Cornwallis.
Clinton published a Narrative of the war, in an attempt to clear his reputation. He was, wrote Major Wemyss who served under him, "an honourable and respectable officer of the German school; having served under Prince Ferdinand of Prussia and the Duke of Brunswick. Vain, open to flattery; and from a great aversion to all business not military, too often misled by aides de camp and favourites." The vitriolic Colonel Charles Stuart called him "fool enough to command an army when he is incapable of commanding a troop of horse." Mackesy argues that he was "a very capable general in the field." Wemyss pointed out Clinton's real weaknesses: his interests were narrow, and he was crippled by self-distrust. In a station where political and administrative questions crowded in on the commander, he lived retired with very poor staff work that insulated his mind from the realities of American opinion and exaggerated the value of loyalists. He was a difficult colleague, for he was jealous, hot tempered, and quick to take dislikes and to notice slights. At the beginning of 1778 he had been bespattering Howe with abuse; and his command was marked by endless quarrels with the admirals on the station.
Clinton was re-elected to Parliament in 1790, and he was promoted to full General in October 1793. The following July he was appointed Governor of Gibraltar, but he died in Cornwall, England before assuming that post.
Henry Clinton had two sons who continued the family tradition of high command: General Sir William Henry Clinton (1769–1846), and Lieutenant-General Sir Henry Clinton K.B. (1771–1829).