Leftwich was educated at the
University of Cape Town where he was active in student politics. For two years, 1961–1962, he was president of the
National Union of South African Students (NUSAS) which opposed the government's
apartheid policies. The scholar and author
R.W. Johnson heard Leftwich speak at a NUSAS meeting and recalled almost sixty years later that "he spoke with a charm and a power that I have seldom seen equalled". After leaving his NUSAS office Leftwich became involved in radical underground opposition to the regime. He became best known for turning state evidence against his comrades in a 1964 bomb plot with the
African Resistance Movement (ARM). He and a small group of fellow students blew up a Cape Town suburban railway signal cable after which he was detained on 4 July 1964. He collaborated with the police under threat of torture, and other members of the movement were arrested and imprisoned. Stephanie Kemp, who spent time in jail for her involvement in the bombing, stated on her Facebook page that she had "gone through a painful journey of reconciliation with him over 12 or more years. He was the same person, although he could never forget his fall almost 50 years ago. I remember him for his courage in taking on the apartheid state at such a young age and his fortitude in bearing the notoriety of stumbling in the face of enormous state repression." Author
Hugh Lewin, who was also jailed for his role, wrote of his path to reconciliation with Leftwich in the book
Stones Against the Mirror: Friendship in the Time of the South African Struggle. ==Later life==