Josef Schleinkofer started boxing as a youth, joining the local sports club TSV 1860 München (Munich). He was German champion as a featherweight in 1931 and 1932. His second place in Los Angeles behind the Argentinian Carmelo Robledo also earned him the 1932 European title. Schleinkofer was a member of the German team in several international meetings. In 1935 he turned professional for two years and had several bouts in South America, retiring after losing his last fight in February 1937 in Buenos Aires. He was a carpenter apprentice in 1932, while in later life, he returned to his native München.