Smithson was nomadic in his lifestyle, travelling throughout Europe. As a student, in 1784, he participated in a geological expedition with Barthélemy Faujas de Saint-Fond, William Thornton and Paolo Andreani to Scotland and especially the Hebrides. He was in Paris during the French Revolution. In August 1807 Smithson became a prisoner of war while in Tönning during the Napoleonic Wars. He arranged a transfer to Hamburg, where he was again imprisoned, now by the French. The following year, Smithson wrote to Sir Joseph Banks and asked him to use his influence to gain release; Banks succeeded and Smithson returned to England. He never married or had children.