BACKGROUND: Effective interventions for reducing the consumption of products that harm population and planetary health often lack public support, impeding implementation. Communicating evidence of policies' effectiveness can increase public support but there is uncertainty about the most effective ways of communicating this evidence. Some policies have multiple benefits such as both improving health and the environment. This study assesses whether communicating evidence of multiple versus single benefits of a policy increases its support. METHOD: Participants (n = 4616) nationally representative of the British population were randomised to one of 24 groups in an online experiment with a 4 × 3 × 2 between-subjects factorial design. The messages that participants viewed differed according to the evidence they communicated (no message, effectiveness for changing behaviour, effectiveness for changing behaviour + one policy benefit, effectiveness for changing behaviour + three policy benefits), type of policy (taxation, availability) and the target behaviour (consumption of energy-dense food, alcohol, or meat). The primary outcome was policy support. RESULTS: In a full factorial ANOVA, there was a significant main effect of communicating evidence of effectiveness on policy support, which was similar across policies and behaviours. Communicating three benefits increased support relative to communicating one benefit (d = 0.15; p = 0.01). Communicating one benefit increased support compared to providing evidence for changing behaviour alone (d = 0.13; p = 0.004) or no message (d = 0.11 p = 0.022). CONCLUSION: Communicating evidence of a policy's benefits increases support for policy action across different behaviours and policies. Presenting multiple benefits of policies enhances public support.