Petrus Johannes Truter, physician, judge and civil servant, was the son of Petrus Johannes Truter senior (1747-1825) and his wife, Johanna E. Blankenberg. The Truters were a leading Dutch family at the Cape and featured prominently in the legal profession. His sister Anna M. Truter was married to the explorer John Barrow*. Truter studied medicine at the Univeristy of Leiden in the Netherlands from 1795, qualifying as Doctor of Medicine (MD) in 1798. He returned to the Cape in 1799 and on 14 September 1800 married Catharina A. Schindeler, with whom he had nine children. He did not practice medicine at the Cape, and was not registered to do so.
From 1 October 1801 to April 1802 Truter led an expedition to the country of the Tlhaping (known to the early settlers as the Beriqua), north of the Orange River, accompanied by Dr W. Somerville* and including the artist Samuel Daniell*. Although one object of the expedition was to explore a region as yet unknown to the colonists, its main aim was to barter cattle in order to alleviate the chronic food shortage at the Cape. The "Expedition to the Beriqua", as it was called, reached the Sak River, beyond the colonial boundary, on 21 October and arrived at the south bank of the Orange River near present Prieska on 1 November. They proceeded as far north as Lattakoo, some distance north of the Kuruman River, becoming the first Europeans to meet and describe the southern Tswana. Extensive negotiations led to the exchange of only some 200 head of cattle, but much was learned about the region and its people. The official report of the expedition was kept by P.B. Borcherds, supervised by Truter. A description of the expedition by Truter and Somerville, entitled "An account of a journey to Leetakoo, the residence of the chief of the Booshuana nation...", was published as an appendix in John Barrow's* book A voyage to Cochinchina in the years 1792 and 1793... (London, 1806). Barrow used the information gathered by the expedition to improve his map of southern Africa.
When vaccination against smallpox was introduced at the Cape in 1804 Truter was appointed secretary to the commission of twelve medical men, led by Dr R. de K. Dibbetz*, who had been appointed by the authorities to control the vaccination process. He was the youngest of the twelve members of the commission, and the only one born at the Cape. After the Cape became a British colony again in 1806 a Vaccine Commission was appointed in January 1807, with Truter as its secretary. In 1811 he was appointed secretary to the Burgher Senate and in May 1814 became customs officer in Simonstown, a post he held for five years. He then returned to Cape Town and in April 1819 was appointed a member of the Court of Justice. After this court was dissolved in 1827 he became civil commissioner of the Worcester district from September 1828 until he retired in April 1849. In 1824 he became a foundation member of the South African Literary Society, but Governer Somerset refused permission for the society to function. Truter's diary reveals his interested in, and knowledge of, plants, climate, geography, and the rock art of the Cedarberg. He also experimented with the cultivation of cotton, pineapples and rice.