Pieter Oranje, civil servant, architect and plant collector, was the supervisor of public works in Barberton, South African Republic (Transvaal) in 1888 and in December that year was appointed to supervise the completion of the local jail and associated outbuildings. By 1889 he was also Barberton's claims inspector. He applied for naturalization as a citizen of the Republic in September 1891. By February 1893 he held the additional position of inspector of roads. He drew up plans for a new school building at Barberton in 1898. In 1901, just after the administration of the Transvaal had been taken over by the British during the Anglo-Boer War (1899-1902), he was appointed as a clerk in the office of the district commissioner at Barberton.
On 8 July 1904 Oranje was appointed as a forest ranger in the Department of Agriculture of the Transvaal Colony, stationed at Barberton. He collected plants in the neighbourhood of the town for the Transvaal Museum. Most of his specimens are now housed in the National Botanical Institute, Pretoria. Some of his plants, including the type of Schotia transvaalensis (the Dwarfboerboon) are in the herbarium of the Royal Botanical Gardens at Kew, England.
In 1913 Oranje was a beacon inspector in the Department of Mines of the Union of South Africa. In 1925 he bought the farms Wilsonvale 176 and Vlottenburg 57 in the Barberton district. In September 1894 he married Evelyn Mary Treadwell, but she died the next year. He then married Maud Mary Hardwick in September 1897.