Blackwood, Sir Henry (1770–1832), vice admiral, was born 28 December 1770 at Ballyleidy, Upper Clandeboye, Co. Down, seventh son of Sir John Blackwood (qv), 2nd baronet, and Dorcas Blackwood (née Stevenson), afterwards 1st Baroness Dufferin and Clandeboye. At the age of 11 he joined the navy as a volunteer; he served as a midshipman under Admiral Cosby in the Mediterranean and was promoted lieutenant in 1790. While in Paris (1792), he was denounced as a spy and had to flee for his life. After the outbreak of war he served on the frigates Active, Invincible, and Megaera, and was promoted senior lieutenant 1 June 1794. Promoted captain (2 June 1795), he commanded the 28-gun frigate Brilliant and bravely held off two French 44-gun frigates near Teneriffe in July 1798. A highly skilful seaman, he could sail frigates faster than any other officer in the Royal Navy. Commanding the 36-gun Penelope in March 1800 in the blockade of Malta, his courage and seamanship led to the crippling and capture of the 80-gun Guillaume Tell which had sailed from Valletta harbour. His conduct was highly praised by Nelson, who became a close friend. He then served with distinction under Lord Keith on the expedition to Egypt and returned to Spithead 19 March 1802. In June 1803 he was given command of the newly built 36-gun frigate Euryalus, and for the next two years served in the Channel and off the Irish coast. Sent to the Mediterranean in July 1805, he commanded the in-shore reconnaissance squadron in Nelson's fleet, and on 19 October he sighted Villeneuve's Franco-Spanish fleet and alerted Nelson. Before battle was joined at Trafalgar, he was present on the Victory, received Nelson's last instructions, and witnessed the final codicil to his will. Nelson trusted him implicitly and allowed him complete discretion in commanding his support ships. He felt Nelson's death keenly, and acted as train-bearer of the chief mourner at his funeral.
While patrolling the Dardanelles in February 1807, Blackwood's ship, the Ajax, caught fire. Over half the crew were lost, but Blackwood survived. He was court-martialled but honourably acquitted. Disappointed not to receive a West Indian governorship, he was given the 74-gun Warspite, which he captained for six years. Commanding the in-shore squadron off Toulon in 1810, he again distinguished himself by driving back a superior French force. In spring 1813 he captured three American privateers and several valuable merchant ships, and in May 1814 he was made captain of the fleet assembled at Spithead for the visit of the allied monarchs to London. The following month he was promoted rear-admiral, and on 1 September 1814 made a baronet. Nominated KCB in August 1819, he served (1820–22) as commander-in-chief in the East Indies, and was promoted vice-admiral in May 1825. He was appointed commander-in-chief at the Nore (1827–30), and a groom of the bedchamber to William IV 25 February 1831. He died from a sudden attack of scarlet fever 14 December 1832 at Ballyleidy. A portrait (1806), by John Hoppner, is held by the National Maritime Museum, Greenwich.
He married three times: in 1795 Jane Mary Crosbie (d. 1798) of Tubrid, Co. Kilkenny – they had no children; in 1799 Eliza Waghorn (d. 1802), with whom he had a son, Sir Henry Martin Blackwood (1801–51), 2nd baronet, capt., RN (1827); and in 1803 Harriet, daughter of Francis Gore, governor of Grenada, with whom he had two sons and two daughters, including Francis Price Blackwood (1809–54), capt., RN (1838).