After his parents divorced, his mother married Creston Clarke, and Harry later adopted his last name (but changed the "a" to an "o," and dropped the final "e" to be able to join the writers' union once he began working as a screenwriter; there was already another Harry Clark).
[1][2] After moving to New York and establishing himself first as a performer (chiefly in vaudeville productions), and second as a playwright, penning a number of works that hit Broadway, he broke into screenwriting in the mid-1930s.
[1] Some of his earliest efforts while under contract at Universal included 1935's Mister Dynamite and Diamond Jim.
[6] He had retired by the 1970s; he died on June 18, 1978, and was survived by his daughter (from his second marriage to actress Mildred MacLeod).
Earlier in life, he had been briefly married to Broadway actress Nora Bayes.