David Greenglass was recruited into Soviet espionage by his wife, Ruth Greenglass, at the behest of his brother-in-law, Julius Rosenberg. The Rosenbergs were executed in 1953 after being convicted of conspiracy to commit espionage with regard to American atomic secrets. Greenglass reportedly shared an interest in Communism with the Rosenbergs. Greenglass would later claim that he lied at the Rosenberg trial in order „to protect himself and his wife, Ruth, and that he was encouraged by the prosecution to do so.“
Born on March 2, 1922, Greenglass married Ruth (née Printz) in 1942, when she was 18 years old. The two joined the Young Communist League shortly before Greenglass entered the U.S. Army in 1943. A machinist at the Army base in Jackson, Mississippi, Greenglass was promoted to sergeant and assigned to the secret Manhattan Project, the wartime project to develop the first atomic weapons. He was first stationed at the massive uranium enrichment facility at Oak Ridge, Tennessee, and later worked at the Los Alamos laboratory in New Mexico. Greenglass humorously related how he slept through the first test of the atomic bomb and made artificial diamonds at the Los Alamos machine shop where he worked.