Scientists are increasingly joining environmental movements. As knowledge producers and influential figures in society, scientists are uniquely positioned to drive change. Here we explore how scientist identity shapes engagement in environmental activism using qualitative and quantitative data from a multinational survey of 329 scientists from 41 countries. Scientist identity content, specifically perception of the science-activism relationship, was a stronger explanatory variable than strength of identification as a scientist. Perceiving a harmonious relationship between science and activism, endorsing environmental stewardship as a scientist’s duty, and believing objectivity and impartiality remained uncompromised by activism, each had significant correlations with engagement. These components formed a composite variable, which remained a robust explanatory variable of engagement even when accounting for the influence of activist identity. Scientists embracing scientist-activist compatibilism were also less inclined to view new technologies as a panacea for the climate crisis. This research underscores the important role of scientist identity content in shaping climate actions and perspectives.