Leu travelled in Norway in 1843 and 1847, and later travelled widely in the Alps. His Norwegian paintings raised awareness in Germany of that country's scenery. He lived for a time in Brussels, then returned to Düsseldorf; in 1855 he received an honourable mention at the Paris Exposition. In 1882 he moved to Berlin, where he became a royal professor and a member of the Academy of Art; he was also a member of the Vienna, Amsterdam and Brussels Academies. He received several gold medals in Berlin and was awarded the Belgian Order of Leopold.