Lohner initially trained as a commercial artist, while also taking private acting lessons. He made his acting début in 1952 at the Stadttheater Baden. He also appeared in Opera buffa at the Stadttheater Klagenfurt. From 1953 to 1963 he appeared in various productions of the Theater in der Josefstadt, as well as making numerous film appearances.
Further engagements in Berlin, Munich, Hamburg, Düsseldorf and Zurich followed. Between them he appeared at the Burgtheater, and at the Salzburg Festival several times, taking the roles of "Death", "The Devil" and "Jedermann" in Hugo von Hofmannsthal's play Jedermann (which by tradition is performed every year). He made his film debut in 1955 in Josef von Báky's Hotel Adlon. From 1963 he was active in television as actor and director.
Lohner married and divorced the German actress Susanne Cramer twice. He then married the German actress Karin Baal, with whom he has a daughter, actress Therese Lohner.