On 5 August 1785 he transferred to the Dutch East India Company, retaining his rank, and in February 1786 was appointed Company building inspector under Captain Sebastiaan Willem van de Graaff, son of the Governor. In August 1786 he was chosen to direct the School of Cadets started by the Governor; his duties included being Professor of Mathematics and Military Science. Thibault settled in a place that came to be known as the Brand House, and later the Wale Street police-station. Between 1786 and 1790 Thibault designed all new public buildings and a number of private houses. From this date on Thibault's work is associated with that of Anton Anreith, a young sculptor and woodcarver from Freiburg, who had arrived as a soldier in the company's service in 1777, and with Hermann Schutte, a young architect and builder from Bremen who arrived in 1789. In 1790 the Dutch East India Company was virtually bankrupt and all work on public buildings and fortifications was stopped. Private commissions, however, continued unabated. In 1788 Thibault had been promoted from lieutenant of engineers to captain and by 1795 to chief military engineer. Before and during the British occupation of the Cape, Thibault was obliged to carry out orders from Colonels de Lille and Gordon, which as an accomplished military strategist, he knew to be unsound.