In 1854 he left Germany to take on the role of Professor of Physics in Basel, nine years later he moved to Braunschweig and in 1866 to Karlsruhe. In 1871 he accepted the chair of physical chemistry at Leipzig. The attention he had paid to chemistry in the earlier part of his career enabled him to hold his own in this position, but he found his work more congenial when in 1887 he was transferred to the professorship of physics. With Rudolph Franz, Wiedemann developed the Wiedemann–Franz law relating thermal and electrical conductivity in 1853.