Herbert Ernest Hart was born in New Zealand at Taratahi, near Carterton, Wairarapa, on 13 October 1882. He was the son of Mary Ann Reid and her husband, William Hart, a labourer. Between 1887 and 1895 Hart attended Dalefield and Carterton primary schools. After leaving school he did clerical work in Carterton and attended night classes in Masterton. Early in 1902 Hart enlisted in the Ninth New Zealand Contingent for the South African War. It arrived in South Africa in April but did not see any action before the war ended on 31 May. Hart reached the rank of lance sergeant before the contingent returned to New Zealand in August 1902.
He then undertook part-time legal studies. On 8 April 1903, at Carterton, he married Minnie Alma Eleanor Renall, daughter of a local farmer. Their marriage produced a family of three daughters (one of whom died in infancy) and a son. Hart qualified as a barrister and solicitor in 1907 and began practising in Carterton with Thomas Maunsell.
In 1907 Herbert Hart was elected a lieutenant in the newly formed Carterton Rifle Volunteers. In 1911 he was promoted to captain in the 9th Regiment (Wellington East Coast Rifles); the following year he was promoted to major. In 1914 Hart transferred to the 17th (Ruahine) Regiment. He has been credited with introducing the lemon-squeezer hat into service with this regiment.
Hart volunteered for service with the New Zealand Expeditionary Force in 1914 and was appointed second in command of the Wellington Battalion. He left New Zealand with the main body of the force in October 1914, and, after a period in Egypt, landed at Gallipoli on 25 April 1915. On 27 April Hart played an important part in halting a dangerous Turkish attack on the front line at Walker's Ridge. That evening he was shot in the thigh at close range. For his gallantry and leadership during this action he was mentioned in dispatches and appointed a DSO. Hart spent several months in England recovering from his wound.
In August 1915 Hart was promoted to lieutenant colonel; his only comment in his diary was that it would increase the pension his wife would receive 'if I happen to go out'. Early in September he returned to Gallipoli and took command of the Wellington Battalion. He was distressed by the losses the New Zealanders had suffered and by the state of the soldiers. He remained in command of the battalion until the end of the campaign.
After the New Zealand Division arrived in France in April 1916 Herbert Hart continued to add to his reputation as a brave and decisive officer who was both a good operational commander and a capable administrator. Near Armentières, on 1 July 1916, he organised a highly successful trench raid, but suffered a heavy blow when Captain Alexander McColl, his 'bosom friend and right hand man', was killed.
Between October 1916 and February 1917 Hart had brief – but successful – periods as a temporary brigade commander. In March 1917 he was made a temporary brigadier general and given command of the 4th New Zealand Infantry Brigade, which was being raised from reinforcements in England. Hart directed its training, and under his leadership it quickly developed into a highly efficient unit. The brigade performed particularly well during the New Zealand Division's successful attack on Gravenstafel Spur during the third battle of Ypres (Ieper) in October 1917. Hart was profoundly disappointed by the decision in January 1918 to disband his brigade as part of a reorganisation of the New Zealand Division.
Early in February Hart took over command of the 2nd New Zealand Infantry Brigade. A few days later he and virtually all his staff were badly gassed. In early April 1918 he took charge of the New Zealand reserves at Sling Camp in England. Well aware of the 'waste and destructiveness' of the bloody struggle in which he was engaged, he became cynical about the honours and awards received by senior officers. In June 1918, after being made a CMG, he wrote: 'It has been remarked that awards are now served out as rations; be it so no one likes being without his rations'.
Late in July 1918 Hart returned to France and took command of the 3rd New Zealand (Rifle) Brigade. Over the next four months he led it in a series of victorious actions, which began with the battle of Bapaume and ended with the dramatic capture of the walled town of Le Quesnoy. After learning of the armistice on 11 November Hart wrote, 'so it is all over at last Thank God for that. There is no jubilation and no excitement.' In recognition of his distinguished service Hart was mentioned in dispatches four times, awarded the French Croix de guerre and made a CB.
Herbert Hart returned to New Zealand in April 1919 and was discharged from the Expeditionary Force in May. He moved to Masterton and established a new legal firm, which operated there and in Carterton. He was the first president of the Masterton Rotary Club and received the New Zealand Returned Soldiers' Association's highest honour, the Gold Badge, for his work on behalf of former soldiers. Hart was a keen hunter; during the 1920s he was one of the first people to hunt wapiti in the South Island. He also travelled to central Africa on a hunting expedition.
Hart commanded the 2nd New Zealand Infantry Brigade from June 1920 to May 1925, when he transferred to the reserve of officers. He retired with the rank of brigadier general in December 1930.
In early 1931 the New Zealand government appointed Hart as administrator of its League of Nations mandate in Western Samoa. When he took up his new position in April, he was faced by a difficult economic and political situation. He was obliged to introduce tight controls on expenditure, and he succeeded in restoring the territory's finances to a sound footing. Hart seems to have held more enlightened views than some of his predecessors, and took steps – albeit ultimately unsuccessful – to improve relations with the Mau, the Samoan nationalist organisation. The government regarded Hart as a successful administrator who oversaw an improvement in Western Samoa's financial and political circumstances, a view not shared by all sections of Samoan opinion. Hart's services in Western Samoa were recognised in June 1935 when he was made a KBE. The following month he completed his term of office and returned to New Zealand.
In May 1936 Hart was appointed deputy controller of the Imperial War Graves Commission. From Jerusalem he directed work on cemeteries and memorials in Egypt, Palestine, Salonika, Gallipoli, Iraq and Iran. Between mid 1940 and late 1942 he also ran the British Army's grave registration service in East Africa and the Middle East. Hart was commissioned as a lieutenant in the British Army in July 1940 and given the unpaid acting rank of brigadier. He retired from his post with the war graves commission at the end of 1943. After returning from the Middle East, Hart resumed an active role in community life in Masterton. In December 1966 Lady Hart died, and on 5 March 1968 Sir Herbert Hart died at his home in Masterton. He was survived by two daughters and a son.
Herbert Hart was one of the New Zealand Expeditionary Force's outstanding leaders. He was an intelligent man, who took an active interest in international affairs. During the mid 1930s he spoke out publicly about the threat posed by Europe's fascist regimes. He was a resilient individual, with a dry sense of humour, whose personality combined a genial and considerate disposition with a resolute will.