In 1951, he married Ruth Narowlansky, with whom he had two children, Carl and David; they were divorced in 1964. He married Danielle Salti in 1964; the couple was divorced in 1978. He married Mary Ellen Curtis in 1979. He died on March 21, 2012. In 1973, Horowitz was one of the signers of the Humanist Manifesto II.
