Dantine's father was the head of the Austrian railway system. As a young man, Dantine became involved in an anti-Nazi movement inVienna. In 1938, when he was 21 years old, the Nazis took over Austria during the Anschluss. Dantine was rounded up, with hundreds of other enemies of the Third Reich, and imprisoned in a Nazi concentration camp outside Vienna. Three months later, using their influence, his parents got his release and immediately sent him to California to live with a friend. Both his parents would later die in a Nazi concentration camp.
He began his U.S. acting career at the Pasadena Playhouse, where he was spotted by a talent scout and signed to a Warner Bros.contract. Dantine spent the early 1940s there, appearing in International Squadron (1941) with Ronald Reagan, Casablanca (1942),Edge of Darkness (his first lead role), Mission to Moscow, Northern Pursuit (all 1943), Passage to Marseille, The Mask of Dimitrios (both 1944), Hotel Berlin, and Escape in the Desert (both 1945).
Dantine was also loaned out to other film companies for two notable films in 1942. To Be or Not to Be and Mrs. Miniver were both released in 1942. In 1944 exhibitors voting for "Stars of Tomorrow" picked Dantine at number ten.
Dantine appeared as Dolokhov in King Vidor's War & Peace in 1956. His last screen appearances were in three films he executive produced including, Bring Me the Head of Alfredo Garcia (1974), and The Killer Elite (1975), both directed by Sam Peckinpah, and The Wilby Conspiracy.
From 1947 to 1950, he was married to Charlene Stafford Wrightsman (1927–1963), the younger daughter of Charles B. Wrightsman, an oil millionaire whose collection of French furniture and decorative arts fills several galleries at the Metropolitan Museum of Art. They had one son, Dana Wrightsman Dantine. In 1952, Charlene Dantine married the American society columnist Igor Cassini. His second marriage was to Nicola Schenck, daughter of Nicholas Schenck, one of the founders of Loews. Nicola subsequently acted as Niki Dantine, and had two children with Dantine. Helmut Dantine died from a heart attack at the age of 64.