The public expression of opinions (and related communicative activities) hinges upon the perception of opinion consensus. Current explanations for opinion consensus perceptions typically focus on egocentric and other biases, rather than functional cognitions. Using self-categorization theory we showed that opinion consensus perceptions flow from cognitions regarding the fit between issues and group prototypes. Strong normative fit enhanced perceptions of ingroup opinion consensus (Experiments 1 and 2), and consensus perceptions varied as a function of comparison outgroups (Experiment 3), ingroup prototype salience (Experiment 4), and levels of identity threat (Experiment 5). Self-categorization theory has the potential to integrate a variety of cognitive and motivational processes to provide a comprehensive explanation for opinion consensus perceptions.