Joan (or Johan) Bax, entitled van Herentals, entered the service of the Dutch East India Company as a soldier and in 1657 was sent to the East on the same ship as Hendrik A. van Reede*, whom he befriended. They called at the Cape in April that year. Bax became an ensign in 1659 and achieved the rank of Captain in 1662. He and van Reede fought together on the Malabar coast (India), where Bax remained until 1669 when he was appointed Van Reede's successor as Sergeant-Major of Ceylon. That year he married Aletta Hinlopen, who was a niece of Joan Huydecoper van Maarsseveen, burgomaster of Amsterdam and a director of the Dutch East India Company. Huydecoper was interested in natural history and Bax regularly sent him natural curiosities from Ceylon, including live plants and animals. Bax became commander of Galle, Ceylon, in 1672. In November 1674 he was promoted to Governor of the Cape of Good Hope, probably through Huydecoper's influence, but owing to slow communications he arrived on the Voorhout only on 3 January 1676. He took up his duties on 14 March that year, succeeding Isbrand Goske.
Huydecoper founded botanical relations between the Netherlands and the Cape during the governorships of Bax and his successor, Simon van der Stel*. Bax sent him natural history specimens from the Cape, including live birds and mammals, skins, chests of seeds and bulbs, and two boxes of herbarium specimens; also a set of water colour paintings of plants by an unknown Cape draughtsman. In return he received seeds of Dutch trees. He sent material also to Prince William III, Stadtholder of Amsterdam: bulbs, plants and wild almond trees in May 1676, and in March 1677 plants and live animals, including monkeys from Madagascar and a young rhinocerus. The latter died at sea and the skin was presented to Leiden University.
During Bax's term at the Cape stock breeding was expanded and grazing rights were granted for the first time, to free burghers in Hottentots Holland. Bax also sent out sea expeditions along the east and west coast. In October 1678 the Lords XVII appointed him Governor of Ceylon and extraordinary councillor of India, but by then he had already died at the Cape of a chest ailment.