John Robert Dunn was born in Port Alfred, South Africa in ca.1833, son of Robert Newton Dunn and Ann Biggar, and in 1836 the family moved from Port Alfred to Port Natal. In 1847 Dunn's father was killed and, after his mother's death in circa 1851, Dunn and his brother and sisters moved to Cape Colony.

In 1856 Dunn took part in the battle of Ndondakusuka, where he fought on Mbulazi's side against Cetewayo. On a later hunting expedition in Zululand Dunn met Cetewayo for the first time and, even though Dunn had been on his opponent's side, Cetewayo was impressed by the enterprise and fearlessness Dunn had shown during the battle and he persuaded Dunn to settle in Zululand as his advisor. Cetewayo allowed Dunn to choose an area over which he would have autonomous power and in 1857 Dunn selected the uninhabited region of Ngoye.

Through liaison with Natal, Dunn kept Cetewayo informed about developments beyond the borders of his country and did his best to establish good relations with the British authorities. When relations between Cetewayo and the British government deteriorated, Dunn tried to avert war which led to a breach between him and Cetewayo. Dunn took the side of the British and, through his knowledge of the terrain and the disposition of every tribal chief, rendered outstanding service as an intelligence officer during the Zulu War in 1879 for which he was well rewarded. After the war, as one of the thirteen nominated chiefs ('thirteen kinglets'), Dunn obtained jurisdiction over the southern part of Zululand.

However, in early 1883 the exiled Cetewayo was reinstated in the central part of Zululand and Dunn's area was included in a 'Zulu Reserve' under a British resident. Dunn's jurisdiction was considerably curtailed and the hostility of the Usutu (adherents of Cetewayo) flared up against him. In Natal, antipathy towards Dunn's role in Zululand also grew and, after Dunn had provided military aid to Zibhebhu in the final blow against Cetewayo (which resulted in Cetewayo's death at Eshowe in 1884) even the authorities in Natal regarded him with scepticism and Dunn lost his prestige as a political figure. Dunn died at Moyeni, near Eshowe, Zululand, on the 5 August 1895.