Seymour was born in Brooklyn, New York, on July 20, 1915, the son of William Berkowitz and Jennie Romer.
[1] Seymour enlisted in the United States Army in 1941, and listed his occupation at that time as a writer, reporter, and editor.
At some point after serving in World War II, he moved to Los Angeles and began writing film scenarios; his first effort was on 1947's Hemingway adaptation, The Macomber Affair.
[2] In California, he met and married fellow writer Connie Lee, who wrote several of Westerns and B-movies for Columbia Pictures.
Bennett and Lee were both blacklisted as Communists during the 1950s after being named by screenwriter David Lang, at which point their careers in Hollywood came to an end.