Essex graduated from St. Johns University in 1936.
Essex started his career as a screenwriter at Columbia Studio, Hollywood, California in 1945. Since 1950, he worked at Radio-Keith-Orpheum Pictures, Hollywood. Since 1955, he went to Universal Pictures, Universal City in California and worked there for 10 years.
He also worked as a screenwriter at Warner Brothers, Burbank in California since 1955 till 1960, and as a writer at Metro Goldwyn Mayer, Culver City, California from 1960 to 1965. Since 1968, he was a screenwriter, story editor at Warner Brothers, Burbank, California.
Essex was a Democrat.
Essex served as corporal Army of the United States from 1942 to 1945.
Essex married Lee Berman on June 22, 1945. They have children: David and Sarah Madlene.