Social movements have the power to drive large-scale social change but the effectiveness of disruptive tactics in achieving this change is uncertain. To shed light on this debate, we conducted nationally representative surveys before and after a week-long disruptive campaign to block London’s M25 motorway (November 2022) by the protest group Just Stop Oil (n = 1,415). Our results suggest that increased awareness of a radical group as a result of a highly publicized non-violent disruptive protest can increase identification with and support for more moderate climate groups (here, Friends of the Earth) in the span of only 2 weeks. Our study provides new insights into the dynamics of social movements and the role of radical protest in driving change. The positive radical flank effect observed here suggests that non-violent radical actions may constitute a largely untapped strategic resource for moderate groups within the broader climate movement. Disruptive protests by environmental organizations have made news headlines in recent years, with attendant conversations about their efficacy. This study finds evidence that such actions increase support for moderate climate groups on climate policy.