Born in Cape Town in 1920. In the late 1930s while still at school he became an active member of the Communist Party, speaking at public meetings and selling the weekly newspaper, The Guardian. He studied at the University of Cape Town and became an architect. In 1946 he was charged with sedition, arising from the 1946 miner's strike. In 1948 he became an active opponent of the policies of the National Party. After the passing of the Suppression of Communism Act he became Chairman of the Forum Club, a multi-racial political discussion club.
He was arrested on 5 December 1956 on charges of treason arising from his involvement in the Congress of the People and the adoption of the Freedom Charter. After being acquitted and after the Sharpeville massacre in 1960, Horvitch escaped to Botswana and from there made his way to London. During the Treason Trial he did a number of sketches of the various trialists which forms the basis of the Museum Africa's present exhibition. He drew the sketches during their lunchtime breaks, and was encouraged to do so by Ruth First, who was reporting on the trial for the papers. She needed pictures but no cameras were allowed in the courtroom, therefore she relied on Horvitch for some pictures. He went into exile in Britain, and is now living in London.