We are facing an emergency that encompasses the entire biosphere, with devastating consequences for both humans and the natural world on which we depend. As the climate and ecological crises accelerate, scientists are coming to terms with failings inherent in the modes of action we have used to engage society about their ongoing and future effects. Life scientists — including biologists, medical scientists, psychologists and public health experts — are no exception. Countless scientific articles, surveys, reports, and methodological advances have enabled exceedingly detailed assessments of the scale and rate of biological devastation, and its consequences for human health. Yet, we have failed to motivate governments and society as a whole to initiate the transformative change required to avoid further catastrophe. Here, we attempt to explain why our current modes of academic behaviour are undermining our own scientific recommendations, and emphasise the need to change the tactics we have used to effectively engage with society. We present a case for embracing activism in our scholarly responsibilities — including outreach, teaching and research — and to adapt these to the strategic logic of civil resistance. We then describe a number of past and present examples of scientist activism: a practice that is not new, but is in dire need of a radical revival.