John Roxburgh was the illigetimate son of Dr William Roxburgh* and was educated at the Tranquebar Mission, Madras (now Chennai), India. He arrived in the Cape Colony from England in 1798 with his father and the latter's wife. The elder Roxburgh stayed to collect plants until late in 1799. Lady Anna Barnard (1999) met John in April 1799 and described him as "a tall lad of 17 - who is painting flowers and butter flys like his father" (Vol. 1, p. 118). His father intended to leave him at the Cape as a seedsman to supply plants and seeds to the Calcutta (now Kolkata) Botanic Garden, of which the elder Roxburgh was the superintendent. John stayed at the Cape until about 1804. Formal permission for him to remain in the Colony was granted only in November 1801. In April 1803 his property was attached by the Chamber for Regulating Insolvent Estates to pay his debts. On 20 November 1803 he signed the oath of submission to the newly established Batavian Republic.
John sent specimens, particularly heaths, also to Sir Joseph Banks* (these are now in the Natural History Museum, London), and a large collection to A.B. Lambert of London (now in the Conservatoire et Jardin botaniques, Genève, Switzerland). Unlike the plants collected by his father, John's specimens usually lack the date and locality of collection. After his return to India he worked at the Calcutta Botanic Garden as overseer of the Indian flower painters that his father employed. During 1810-1811 he collected plants at Chittagong (now in Bangladesh). In July 1815 he was dismissed from his post by Dr N. Wallich*, who was acting superintendent of the botanic gardens at the time, but was reinstated by James Hare in 1816. He was dismissed again by Wallich, then superintendent, in March 1819.