An admiral, born at Dundalk on 8 July 1819, was the eldest son of Henry McClintock, formerly of the 3rd dragoon guards, by his wife Elizabeth Melesina, daughter of the Ven. George Fleury, D.D., archdeacon of Waterford.
He entered the navy in 1831 and passed his examination in Oct. 1838; but promotion at that date was slow and uncertain, and McClintock remained a mate for nearly seven years. He was made lieutenant on 29 July 1845, when serving in the Gorgon on the South American station, and a few days later was moved into the Frolic, sloop, on board which he served for two years in the Pacific.
On 7 Feb. 1848 he was appointed to the Enterprise, Captain Sir James Clark Ross, for a voyage to the Arctic; and in Feb. 1850 he was chosen to be first lieutenant of the Assistance, proceeding on a similar voyage of discovery. In these expeditions he established his reputation as an Arctic traveler, more especially by making an unprecedented sledge journey of 760 miles in 80 days in the winter and spring of 1851, when the Assistance was frozen up at Griffith Island. On his return home be received his promotion to commander, dated 11 Oct. 1851.
In Feb. 1852 a larger Arctic expedition of five ships was fitted out and placed under the command of Captain Sir Edward Belcher. Two of the ships had auxiliary steam power, and McClintock was given the command of one of these, the Intrepid, which was officially described as tender to the Resolute, Capt. Kellett, under whose immediate orders he was. The Intrepid wintered on the south side of Melville Island, whence many sledge expeditions were sent out. McClintock himself made a journey of 1210 geographical miles in 105 days, during which he examined and charted the west coast of Prince Patrick Island and Ireland's Eye. The comparative perfection to which Arctic sledge travelling attained was in great measure due to improvements introduced by McClintock. In the summer of 1854 Belcher decided to abandon the Intrepid and three other ships, and the party returned home in the North Star and two relief ships. On 22 Oct. 1854, a day after McClintock received his promotion to captain, Dr. Rae arrived with the first certain intelligence of the fate of Franklin's expedition. The Admiralty was satisfied of the truth of the news and took no action to confirm it, but Lady Franklin determined on a search expedition. For this purpose she bought the Fox yacht and had her fitted out, principally at her own cost, giving the command to McClintock who, like the other officers of the expedition, offered his services gratuitously. McClintock published in 1859 an account of this service, entitled The Voyage of the Fox in the Arctic Seas : a Narrative of the Fate of Sir John Franklin and his companions, a work which has gone through many editions. The expedition returned to England in 1859, bringing with it the written memorandum of Franklin's death, of the abandonment of the ships, and of the fate of the whole party. In recognition of his success McClintock was allowed by the Admiralty to count the period of his command of the Fox as sea-time, and in 1860 he was knighted.
From Feb. 1861 to Dec. 1862 McClintock commanded the Doris, frigate, in the Mediterranean, and in Nov. 1863 commissioned the Aurora for service with the Channel squadron. In her he cruised in the North Sea during the Danish war of 1864, and on 9 May of that year, by his presence at Heligoland, prevented the development of what might have been a serious problem in international law. From 1865 he was for three years commodore in charge at Jamaica, and on 1 Oct. 1871 he reached flag rank. From April 1872 to May 1877 he served as admiral superintendent of Portsmouth Dockyard, and on 5 Aug. 1877 was promoted to vice-admiral. In Nov. 1870 McClintock was appointed commander-in-chief on the North America and West Indies station, where, with his flag in the Northampton, he remained for the customary three years. This was his last active service. In Feb. 1884 he was elected an elder brother of the Trinity House, and on 7 July of the same year reached the rank of admiral, one day before being overtaken by the age for retirement. He was created a K.C.B. in the birthday honours of 1891.
McClintock offered himself as candidate for Drogheda at the general election of 1868, but withdrew in consequence of dangerous rioting. He died in London on 17 Nov. 1907, and was buried at Kensington cemetery, Hanwell. He married in 1870 Annette Elizabeth, second daughter of Robert Foster Dunlop of Monasterboice, co. Louth. One son, John William Leopold, entered the navy and was promoted commander in 1905.
Two portraits of McClintock, painted by Stephen Pearce, are in the collection of Arctic explorers at the National Portrait Gallery ; one was painted in 1856. A third portrait by Frederick Yates (1901) belongs to Lady McClintock.