Sustainable consumption practices can drive environmental and societal benefits. One way of steering consumers in a desired direction is through the social proof principle, which posits that consumers are more inclined to exhibit a target behavior if they believe that many others already engage in said behavior. We conducted an online experiment ( N = 376; US sample) to test whether reliance on social proof (vs. control) increases consumers' pro-environmental responses, and whether trait conscientiousness moderates this interplay. All included social proof messages outperformed the control condition, regardless of whether they were based on majority (vs. minority) information or dynamic (vs. static) social norms. Additionally, the social proof effect was particularly pronounced among consumers scoring low (vs. high) in trait conscientiousness, with these consumers typically exhibiting the least pro-environmental behaviors according to previous research. Taken together, the current findings carry important implications regarding ways to tackle climate change.