Born in Waukegan, Illinois of German descent to Mickey Snr. and Pearl Hicks, he gained fame as child actor in the 1930s and appeared opposite Conrad Nagel and Leslie Howard, amongst others. His first fame came when he won the role auditioned for by 100 other child actors in playing Beau Wilkes, the son of Leslie Howard and Olivia de Havilland's characters Ashley Wilkes and Melanie Hamilton in Gone with the Wind in 1939. He later went on to appear in Juarez (1939) opposite Bette Davis, as the adoptive son of John Wayne in Red River, Broken Arrow starring James Stewart and in A Streetcar Named Desire (1951), a role in which he was reunited with Vivien Leigh a dozen years after they first worked together in Gone with the Wind. In A Streetcar Named Desire, Kuhn played a sailor who directs Leigh's character Blanche to the correct streetcar which will take her to her sister's neighborhood at the beginning of the film. He is the only actor to share screen time with Leigh in each of her Oscar-winning performances.