From 1757 Jean-François Rousseau was deputy director of the French East India Company at Basra while conducting diplomatic and trade missions in Persia.
After the death of Claude Pirault, the Company's director, Rousseau took over his duties but not his title and continued successfully to defend French interests against competing claims, negotiated Persian-Ottoman relations and protected the rights of French resident aliens in the area.
He was accompanied by the botanist André Michaux and in Aleppo also joined up with abbé Pierre-Joseph de Beauchamp, who was not only an astronomer but also vicar general of Baghdad.
Rousseau, Michaux and de Beauchamp travelled with the caravan from Aleppo to Baghdad in September and October 1782.
Rousseau spoke seven foreign languages (Arabic, Persian, Turkish, Armenian, Portuguese, Italian and English) and was a major orientalist.