Nonviolence is an important element of sustainability for three main reasons. One is that nonviolent actions, including Australia's Franklin River campaign, anti-nuclear blockades at Roxby Downs and Jabiluka, northern NSW old-growth forest blockades, and climate actions against coal seam gas and coal extraction, have long been effectively used by environmentalists, conservationists, and preservationists to protect environments from damage and to advocate for more sustainable societies, institutions, systems, and processes. Nonviolent environmental action has also opposed militarism for a range of reasons, one of which is concern about the large environmental footprint of militarism. The third reason why nonviolence is important for sustainability is because it offers an alternative to militarism as a means of national and regional self-defence and the removal of dictatorships, genocidal regimes, and military juntas. This alternative has much lower environmental, economic, and social costs. The article begins with the introduction and methods sections, introduces the 2030 Agenda of the United Nations and 'sustainability' and defines 'nonviolence' and introduces its connection to sustainability. This is followed by the case studies and a discussion of how these nonviolent actions contributed to environmental sustainability. Militarism and its impacts on the environment are described, and nonviolent defence and regime change are presented as viable and less environmentally-damaging alternatives.