Madoc acted on stage with the Welsh Theatre Company playing Thomas Cromwell in a 1962 tour of "A Man for All Seasons" before joining the Royal Shakespeare Company, playing the roles of Iago, Othello and Dr Faust. As a television actor he first gained widespread recognition in two serials, first as the relentless SS Officer Lutzig in the Second World War serial "Manhunt" (1969), and then as the vicious Huron warrior Magua in a serialisation of "The Last of the Mohicans" (1971).