Kaje (or Caje, Cajus) Jesse Stotsboo probably joined the army in the Netherlands and reached the rank of sergeant in the regiment of the Duke of W?rttemberg. He then became a soldier of the Dutch East India Company and spent from 1693 to 1697 in the Dutch East Indies (now part of Indonesia). In September 1698 he was sent to the Cape of Good Hope as commander of the soldiers on the Stad Keulen, the same ship in which the new governor of the colony, W.A. van der Stel*, was travelling to the Cape. Arriving in January 1699 he started training the soldiers of the Cape garrison and soon became commander of the governor's bodyguard, with the rank of sergeant. He surveyed the farm Vergelegen, which had been granted to Van der Stel on 1 February 1700. The resulting manuscript, Kaart van de verdeeling in vier gedeelten van het land Vergelegen (Map of the division into four parts of the land Vergelegen), dated 1709, went to the archives in the Netherlands (Schunke Hollway, 1898).
In 1700 Slotsboo succeeded Douw Steyn as the Company's land surveyor at the Cape, a post he held until 1718. During that time he surveyed and compiled diagrams of 382 properties (Cape of Good Hope, 1859). He was the first of many military men involved in surveying at the Cape during the eighteenth century. The diagrams that he drew show him to have been an innovative man, for example, he introduced the practise of adding a description of the land surveyed immediately below his diagrams. He also developed the technique of depicting different areas of land within a single diagram, thus indicating clearly what was being granted. On 27 November 1714 he and the engineer Cochius became the first persons to take the oath of the surveyor at the Cape.
Slotsboo was promoted to ensign in 1704 and was given additional duties as commissioner for petty cases (1703) and for matrimonial affairs (1706). On 23 December 1703 he married Anna R. Hartz, with whom he had three surviving children. After her death he married Aletta Beck in 1715. In 1707 he became overseer of the slaves in the Company's forests and the next year was promoted to lieutenant. His competence is indicated by the fact that, in addition to his other duties, he supervised the Company's brickworks, masons and carpenters, and from 1708 served on the Council of Policy. In 1710 he became chairman of the matrimonial court and a member of the Council of Justice.
In October 1712, following rumours that the Khoi were attacking settler farmers, Slotsboo was sent to Piketberg in command of an expedition of 181 persons. After proceeding to the Olifants River without meeting any Khoi the force returned to Cape Town. During this expedition he (and probably two of his men) became the first to inscribe their names, and the year 1712, in the Heerenlogement, a well-known cave north of present Graafwater. Slotsboo also inscribed his name on a stone on the neighbouring farm Klipfontein. In April 1713 he was promoted to "captain-lieutenant" and in 1718 succeeded Captain D.M.P. de Chavonnes as commander of the Cape garrison, attaining the rank of full captain the next year. He subsequently became a prominent official at the Cape, serving as president of the court of petty cases, the burgher military coucil and the orphan chamber.