Segrave, Sir Henry O'Neal de Hane (Dehane) (1896–1930), land- and water-speed record holder, was born 22 September 1896 in Baltimore, Maryland, USA, the only child of Charles William Segrave, of the British consular service and later JP for Co. Wicklow and Co. Tipperary, and his first wife, Mary Lucy Harwood (d. 1898), daughter of James Kemp Harwood of the United States Navy and granddaughter of the Rt Rev. James Kemp, archbishop of Maryland. After the death of his mother, his father returned to Ireland (1899) and settled at the family estate in Co. Wicklow, and in 1901 they moved to Kiladreenan, near Wicklow Head. His father was one of the first automobile owners in Ireland, and at the age of 9 he used to drive his father's De Dietrich around the grounds of their house. This marked the beginning of his lifelong fascination with cars, motorcycles, and speed. In 1906 the family moved again, this time to the Belle Isle estate in Co. Tipperary, near Portumna, Co. Galway. His father acquired a motor boat, and Henry used to accompany him on trips around Lough Derg and on the Shannon. He was initially educated by a private tutor and then attended Bilton Grange preparatory school near Rugby before entering Eton (1910).
In September 1911 he was given his first motorcycle for his fifteenth birthday, and in 1913 took part in the army manoeuvres in Co. Tipperary as an unofficial dispatch-rider at the suggestion of a family friend, Col. (later Gen.) William B. Hickie (qv). He was active in the Eton OTC and served as the unit's dispatch-rider. At the outbreak of the first world war he briefly attended Sandhurst before being commissioned into the Royal Warwickshire Regiment. He served in Belgium and France and was present at the battle of Neuve Chapelle (10 March 1915). In May 1915 he was wounded and was sent to England to convalesce. He transferred to the Royal Flying Corps, qualified as a pilot in January 1916, and served with No. 29 Squadron in France, flying DH2 and later FE8 scouts. Promoted to captain, he was shot down and wounded twice, fracturing his ankle badly on the second occasion (July 1916), and it was feared that the foot might have to be amputated. He was operated on by the distinguished surgeon Dr Robert Jones, who inserted a number of silver plates in his ankle, and he returned to duty. He was attached to GHQ in France in 1916, and in 1917 was appointed private secretary to the chief of the air staff at the war office in London. In June 1918 he was posted to Washington as a member of the British aviation mission with the rank of major. He left the RAF at the end of the war, having been mentioned in dispatches.
Still obsessed with fast cars and motorcycles, he determined to become a racing driver and made a modest beginning by being appointed as competition manager to K.L.G. Sparking Plugs in 1920. In 1921 he was accepted by Louis Hervé Coatalen, designer and manager to Sunbeam, as a team driver, and in the same year won the Brooklands 200-mile (320 km) race, competing against his team-mates Kenelm Lee Guinness and Malcolm Campbell. In 1923 he won the European Grand Prix at Tours, and was appointed (1924) head of Sunbeam's London sales department. He became the world record holder for the flying-start kilometre in 1926, achieving 152.33 mph (245.15 kph) on Southport Sands. He continued to race for Sunbeam and won further Grands Prix before retiring from motor racing in 1927 (Boulogne GP, 1923; San Sebastian GP, 1924; GP de Provence, 1925, 1926).
He then decided to devote himself to record-breaking, and on 29 March 1927, at Daytona Beach, Florida, he became the first man to travel at over 200 mph, achieving 203.792 mph (327.97 kph) over the measured mile in a Sunbeam car designed by Coatalen and powered by two 22.5 litre aero-engines. In 1927 he joined the Portland Cement Co., which sponsored his car Golden Arrow, in which he recaptured the land-speed record at Daytona (11 March 1929), achieving 231.446 mph (372.475 kph). After this achievement he was received by President Herbert Hoover and was knighted by George V (1929). In 1929 he joined the Aircraft Investment Corporation as technical adviser, overseeing the design of the Segrave Meteor, an advanced type of monoplane.
In May 1927 he had also begun racing boats, and in his boat Miss England I had made unsuccessful attempts on the water-speed record. He designed and developed a second racing boat, Miss England II, and in June 1930 began a series of attempts on the water-speed record on Lake Windermere. On Friday 13 June 1930 he took the water-speed record, covering a measured mile at 98.76 mph (158.938 kph), beating the record of Commodore Garfield Wood, USN, by 6 mph. While completing another run – during which Miss England II reached an unconfirmed 119.8 mph (192.8 kph) – the boat hit a submerged object at speed and capsized. His engineer, Vic Halliwell, was drowned and Segrave was badly injured, dying a few hours later.
His remains were cremated in a private ceremony at Golders Green crematorium, north London. A memorial service at St Margaret's, Westminster, was attended by a large crowd, over 200 people having to remain outside the church, a measure of the way in which he had caught the public's imagination and affection. His father later scattered his ashes from the Segrave Meteor over the playing-fields of Eton. It became traditional for family and friends to meet at Lake Windermere on the anniversary of his death to hold a remembrance service. In 1930 the Segrave trophy was instituted for achievements in motor sports and record-breaking. Subsequent recipients included Amy Johnson (1932), Sir Malcolm Campbell (1933, 1939), Stirling Moss (1957), and Donald Campbell (1955, 1958).
He married (October 1917) Doris Mary Stocker, actress; they had no children. In 1928 he published The lure of speed, an autobiographical account of his racing and record-breaking career.