The legitimacy of meat-rich diets in Western societies is slowly in decline as the benefits of meat reduction for personal health, ecological welfare, and animal welfare are become increasingly clear. This is mirrored by a surge of campaigns, which rely heavily on social media platforms to legitimize meat reduction among their target audience: meat-eaters. Social Identity Theory suggests that the effectiveness of meat reduction advocacy will depend on the dietary identity of advocates and their rhetorical style. To examine this, we used a 2 × 2 between-participants factorial design in which we exposed meat-eaters (N = 186) to a meat reduction campaign image shared by an advocate on Facebook, where the advocate was portrayed as either a meat-eater (ingroup) or a vegetarian (outgroup), who used either inclusive language ("we can eat less meat") or personal language ("you can eat less meat") to promote meat reduction. Results reveal that the meat-eating (versus vegetarian) advocate was more likely perceived as inconsistent when promoting meat reduction. Higher perceptions of inconsistency were significantly associated with a lower perceived legitimacy of the message for both advocate types, especially when the advocate was a vegetarian. We also found that meat-eaters were more tolerant of a perceived inconsistency when advocates used inclusive rather than personal language. Perceptions of favouritism towards the advocate could explain the conditional effects of perceived inconsistency on message legitimacy. Lastly, we could observe that meat-eaters who perceived the message as more legitimate and identified less as meat-eaters were more willing to eat less meat. Practical implications of our findings are considered.