Since the 1950s, Japanese non-state actors in the international anti-nuclear weapons movement have disseminated the dangers of nuclear weapons, tied to Japanese experiences of the atomic bombings of Hiroshima and Nagasaki in 1945. Coming from the only country that has experienced nuclear attacks, they provide much needed evidence of the humanitarian impacts of nuclear weapons. These actors include survivors of the atomic bombings, commonly known as hibakusha, who have initiated and persistently maintained the humanitarian focus on nuclear discourse for decades. This paper examines their contributions to eyewitness testimonies on the impacts of nuclear weapons and their efforts leading to major milestones in international efforts for nuclear abolition. It also focuses on the roles played by the Japan Confederation of A- and H-Bomb Sufferers Organization (Nihon Hidankyo) and the Japan Association of Lawyers Against Nuclear Arms (JALANA), which made tremendous contributions facilitating the success of the World Court Project in the 1990s and the Humanitarian Initiative in the 2010s that led to the 2017 Treaty on the Prohibition of Nuclear Weapons. Non-state Japanese contributions were, unfortunately, under-recognised, and the successes of international nuclear abolition were often attributed to other international actors. Hence, this paper recognises the contributions of non-state Japanese actors in sustaining the international anti-nuclear weapons movement and achieving the nuclear ban treaty.