John Mackintosh Roberts was born in India, at Bombay, on 31 December 1840, the first child of Mary Mackintosh and her husband, George Roberts, court keeper to the Supreme Court. George Roberts died in 1844, shortly after the birth of their second child, Georgina. Mary Roberts was joined by her sister Jessie, who soon married William Clare, an officer in the army of the East India Company. By 1854 they had returned to Inverness, Scotland, where John Mackintosh Roberts attended the Royal Academy. In 1855 the families, now including three Clare children and two Mackintosh relatives, set off for New Zealand on the Carnatic. The ship reached Auckland on 27 December.
William Clare took up land in the Hunua area, near Papakura. He and John Roberts started clearing the property and selling the timber, but in 1860 Roberts went to the Otago goldfields. After indifferent success he returned two years later. Tension over land had led to conflict in Taranaki, and farms near Auckland came under attack. The Clare homestead was ransacked after the families had sought refuge with William Hay, near the Great South Road. Clare, a captain in the militia, fought in an action close by on 22 July 1863.
The next month Roberts enlisted as a sergeant in William Jackson's newly formed Forest Rangers. The rangers took Gustavus Ferdinand von Tempsky, then a war correspondent, on a sweep through the bush, and shortly afterwards he joined the unit as an ensign. A second company of Forest Rangers was formed in November, with Tempsky in command and Roberts as his subaltern. The Forest Rangers moved south to join Lieutenant General D. A. Cameron's force at Ngaruawahia. Roberts did not take part in the fight at Mangapiko, but was prominent in the actions at Rangiaowhia and Orakau in 1864. After being allocated confiscated Maori land at Harapepe, he applied for leave to try goldmining at Hokitika, but was refused.
After the formation of the Armed Constabulary Roberts was commissioned a sub-inspector (captain), becoming Tempsky's second in command of No 5 Division. The unit was intensively trained at Alexandra (Pirongia) and in June 1868 was sent to Waihi Redoubt, South Taranaki, to assist Lieutenant Colonel T. McDonnell's forces in the campaign against Titokowaru.
At the 3 a.m. stand-to on 12 July the flashes of firing could be seen at the small Turuturumokai Redoubt, some four miles distant. In McDonnell's absence Tempsky ordered the cavalry to hold Waihi while he led the infantry to the rescue. This error of judgement certainly delayed the relief of the beleaguered garrison. Its commander, Captain Frederick Ross, having been killed, Roberts was placed in charge with 33 men.
McDonnell waited only for reinforcements from Wellington before seeking revenge. On 21 August Roberts took part in a flanking movement in the attack on Titokowaru's bush headquarters at Te Ngutu-o-te-manu, while Major William Hunter led a frontal assault. The Maori retreated into the bush, but harried the force on its withdrawal, when No 5 Division evacuated the casualties.
With the addition to his Patea Field Force of a Maori contingent under Te Keepa Te Rangihiwinui, McDonnell planned a new strike. His force set out on 7 September and encountered Titokowaru and his followers at Te Ngutu-o-te-manu. Some firing at an outpost alerted Titokowaru and he disposed most of his force outside the palisades. No 5 Division advanced on the left, and when Tempsky was killed Roberts took command of the division. An order to retreat went astray, and he became separated from the main body. After a night in the bush he successfully brought his men to Waihi next morning.
The force withdrew to Patea, and No 5 Division was disbanded after a mutiny. Roberts went to Auckland to recruit replacements and returned with them to Waverley. Colonel G. S. Whitmore, who had replaced McDonnell, decided to attack Titokowaru at Moturoa on 7 November. The surprise assault failed. Units led by Roberts and Captain F. Y. Goring lost contact with Whitmore, but fought their way out of the bush.
Roberts, who by now had amply demonstrated his courage and reliability, was promoted to inspector (major) on 15 November. At this juncture Te Kooti, who with his fellow captives had escaped from detention in the Chatham Islands, drew attention to the East Coast. Despite the desperate military situation near Wanganui, Whitmore took his troops to Poverty Bay.
Whitmore lacked information on Te Kooti's whereabouts, and ordered Roberts to take 100 men in the Sturt to defend Poverty Bay. Roberts's sailing was delayed, and so he took part in repelling a raid at Te Arai River in December. The Maori withdrew to a strong hilltop position at Ngatapa, which Whitmore invested as far as numbers allowed. A precipice on one side was thought to be impassable. Roberts, second in command, guarded a long flank when a frontal assault was launched in early January 1869. Eventually shortage of food forced abandonment of the pa by way of the cliff. Te Kooti vanished into the Urewera, and the force returned to Wanganui.
Titokowaru, at nearby Tauranga-ika, had built defences even stronger than at Moturoa. Luckily for the troops, the pa was abandoned without a fight. Roberts and his comrades pursued Titokowaru, with skirmishes at Otautu and Te Ngaere, but their services were soon needed again in the east against Te Kooti.
A two-pronged advance on Ruatahuna was mounted in April 1869. Major J. H. H. St John led a largely European force, with Te Whakatohea support, up the Whakatane River. Roberts took a mainly Arawa column via the Rangitaiki and Whirinaki valleys. After some skirmishing the two met as planned, but because of shortage of food soon had to fall back to Fort Galatea. This post also proved untenable, and the whole expedition withdrew to Tauranga.
Te Kooti, en route to try to rally support from Rewi Manga Maniapoto, had surprised a small detachment at Opepe in June. Roberts was dispatched with No 6 Division to occupy Taupo, while McDonnell held the southern shore of the lake with constabulary and kupapa. The latter met Te Kooti in an inconclusive engagement in early 1870, after which he returned to the Urewera.
Roberts had seen the last of open warfare. He remained in charge of a district stretching from Hawke's Bay to Rotorua until 1871. The search for Te Kooti was handed over to his juniors, Gilbert Mair and George Preece, with their Arawa flying columns. While providing them with logistical support, Roberts employed his garrison on building a road and telegraph line from Napier to Cambridge. The establishment of communications in the central North Island ranks high among his achievements.
After transferring to Tauranga, Roberts held command of the district and served as resident magistrate. He married his cousin, Jessie Mackintosh Clare, on 12 March 1872, at Cambridge. They had a family of two daughters and two sons. In 1876, after returning to Opepe, he received the New Zealand Cross at Cambridge. The medal was awarded in recognition of the bravery and judgement shown by Roberts during the engagements at Te Ngutu-o-te-manu and Moturoa in 1868.
In 1878 Roberts shifted to Tauranga. During the following years his powers of diplomacy were tested. He negotiated with the Pirirakau tribe over a land dispute; then in July 1879 he was promoted to lieutenant colonel in the militia and placed in charge of security in Taranaki. Te Whiti-o-Rongomai III and Tohu Kakahi established themselves and their Taranaki followers at Parihaka. There followed a period of strained relations, ending in confrontation between these Maori leaders and John Bryce, the native minister, on 5 November 1881. On this occasion Roberts, with a force of 1,589 men, entered Parihaka, meeting no armed resistance, and arrested the leaders. Although he supported the authority of the government, Roberts was cool-headed and just. His respect for the Maori and his willingness to deal fairly with them as far as he was able was demonstrated when he received Titokowaru at Opunake in 1886.
Roberts's Opunake command ended in 1886, and in February 1887 he was appointed commander of the new New Zealand Permanent Militia. He was based in Auckland but his tours of duty took him as far as Port Chalmers, inspecting the garrisons and new defences at the main ports. In 1888 he was retired, after 25 years as a soldier. Until his final retirement in 1909, Roberts served on two royal commissions and as resident magistrate at Masterton and Tauranga. He died at his home in Rotorua on 12 October 1928.