Born Oskar Josef Bschliessmayer in Vienna, he was an Austrian stage actor, starring in the William Shakespeare repertoire, until his film debut in Der Engel mit der Posaune in 1948. In 1951 he starred in the English language movie Decision Before Dawn, in which he played a German prisoner of war who spies for his captors.
In 1961 he starred in Francois Truffaut's Jules et Jim, and became an international star as a result. He was nominated for an Academy Award for Best Actor in 1965 for Ship of Fools. Other starring roles were in The Spy Who Came in from the Cold, Fahrenheit 451, and The Shoes of the Fisherman. Werner also played the murderer opposite Peter Falk in an episode of the Columbo TV series entitled "Playback" (1975).
Sadly, both his decline as an actor and eventually his death of a heart attack in 1984 were caused by many years of excessive drinking.