He abandoned the idea of entering the Lutheran ministry, and in 1823 went to Paris, at that time, under Silvestre de Sacy, the major European school of Eastern letters. From 1826 to 1833 he was nominally professor at Tübingen, but had permission to continue his studies abroad, and passed some years in London and Oxford. He resigned his chair at Tübingen in 1834, and settled permanently in Paris.
In 1844 he was nominated to the academy of inscriptions, and in 1847 he became professor of Persian at the Collège de France. But his knowledge and interest extended to all departments of Oriental learning. He served for many years as secretary, and then as president of the Société Asiatique.
He died in Paris on 3 January 1876. She died in Paris on 14 May 1883. Madame Mohl wrote Madame Récamier, with a Sketch of the History of Society in France (London, 1862).
Mohl's elder brother, Robert von Mohl (1799–1875), was a well-known jurist and statesman. He was a voluminous writer on economic and political questions.
Another brother, Moritz von Mohl (1802–1888), entered official life at an early age and was a member of the Frankfort parliament, and later of the parliament of Württemberg and of the imperial Reichstag.