Philip Norman Horowitz was born on March 1, 1904, in Mozyr, Minsk Governorate, Russian Empire (now Belarus), and immigrated to the United States around 1905-1906 as a young child with his parents, Morris Horowitz and Anna Schlarman. He worked as a high school English teacher for the New York City Board of Education, including at Seward Park High School, and was reportedly fired in 1952 for insubordination after refusing to sign a loyalty oath. Horowitz joined the Communist Party USA in the 1920s and remained committed even after Khrushchev's 1956 denunciation of Stalin, though he and his wife quit the party that year. He married Blanche Brown, also a schoolteacher, on September 5, 1935, in Manhattan; they met at Communist Party meetings in the early 1930s. The couple resided in various locations in New York City, including Queens (Forest Hills and Long Island City by 1940). They had two children: David Joel Horowitz (born 1939) and Ruth Horowitz. As a member of the Communist Party USA, he raised his son David in a 'red-diaper' household in Queens, New York.