Buttinger was born into a working-class family and left school at age 13 to help support his family. He became a youth movement leader in Austria and, by the age of 24, was secretary of the Social Democratic Party. After being imprisoned for several months in 1934, he became chairman of the Socialist underground and a leader of the anti-Fascist movement. When Germany occupied Austria in 1938, he and his American-born wife Muriel Gardiner fled to Paris, where he was chairman of the exiled Socialists. In 1939, several months before the fall of France, the couple moved to the United States with Gardiner's daughter from a previous marriage, Connie, whom Joseph later adopted.