Robertson became a barrister in 1973 and a QC in 1988. His became well known acting for the defence in the celebrated English criminal trials of Oz, Gay News, the ‘ABC Trial’, The Romans in Britain (the prosecution brought by Mary Whitehouse), the Brighton bombing and Matrix Churchill. Robertson was also threatened by terrorists for representing Salman Rushdie. He has appeared in civil liberties cases before the European Court of Human Rights and in other courts across the world. He sits as an appeal judge at the UN Special Court for Sierra Leone. His latest book, The Tyrannicide Brief, details the story of John Cooke, who prosecuted King Charles I of England in the treason trial that led to his execution.