Kingsley was born Sidney Kirshner on October 22, 1906, in New York, New York. While attending high school, he began writing one-act plays, directing, and acting. He won a scholarship to Cornell University, where he continued to write and direct plays. In 1928, the same year in which he earned his bachelor of arts degree, he won an award for the best student one-act play.

After graduation, Kingley acted with the Tremont Stock Company in the Bronx, New York. Deciding that he would never be a great actor, Kingsley moved in 1929 to California. He worked as a scenario reader in the movie business. At the same time, he continued working on a play called Crisis. This play opened in 1933 in New York under a new title, in White. play was a critical and commercial success both in the United States and London, and it won the 1934 Pulitzer Prize in...