Lieven started his career at theaters in Gera and Königsberg, his first screen role was in the German film Annemarie, die Braut der Kompanie (Bride of the Company) in 1932. During the next four years he appeared in another sixteen films, including the German film adaptation of Charley's Aunt.
Owing to the rise of the Nazi Party in Germany and his wife Tatjana being Jewish, they moved to Britain in 1937. He spent the years of the Second World War (1939 to 1945) though mainly in roles depicting Nazis in British films, not finding them overly challenging as an actor.
Lieven appeared on the London stage in 1939 in the comedy Rake's Progress (not the later Rex Harrison film of the same title), but was largely acting in films (among them The Life and Death of Colonel Blimp, 1943).
Lieven appeared in many cinema productions, and in the year 1940, he was credited in seven, in all of which he played the role of a German.
He was under contract to Rank for five years from 1945. It has been claimed that he only appeared in one film during this contract, Sleeping Car to Trieste. In fact, however, he appeared in several other films for companies controlled by Rank during this period, as part of his contract. These included Marry Me! (1949), which was made for Gainsborough Pictures, which by that date was a subsidiary of Rank.
He returned to Germany in 1951, and appeared in many films made there. He also was in films both in Britain and Hollywood.