In 1948, he participated under Kurt Hirschfeld in the role of the attorney in the premiere of Herr Puntila und sein Knecht Matti.

After World War II, Ammann belonged to the Ensemble of the theatre Kleine Freiheit in Munich.

Ammann began his film career in the 1939 Swiss movie Constable Studer after the novel of Friedrich Glauser, starring Heinrich Gretler.

In 1961, he played in the series Gestatten, mein Name ist Cox with Günter Pfitzmann and Paul Edwin Roth.

[citation needed] Between 1967 and 1977 he achieved great popularity in his most famous role in the German detective series Graf Yoster, where he played the main part of the same name.

Ammann lent his voice in German dubbing Peter Sellers (in John and Julie, 1955) and Lucky Luke (in the animated film Daisy Town, 1971).