We propose that self-essentialist reasoning is a foundational mechanism of the similarity-attraction effect. Our argument is that similarity breeds attraction in two steps: (a) people categorize someone with a shared attribute as a person like me based on the self-essentialist belief that one’s attributes are caused by an underlying essence and (b) then apply their essence (and the other attributes it causes) to the similar individual to infer agreement about the world in general (i.e., a generalized shared reality). We tested this model in four experimental studies (N = 2,290) using both individual difference and moderation-of-process approaches. We found that individual differences in self-essentialist beliefs amplified the effect of similarity on perceived generalized shared reality and attraction across both meaningful (Study 1) and minimal (Study 2) dimensions of similarity. We next found that manipulating (i.e., interrupting) the two crucial steps of the self-essentialist reasoning process — that is, by severing the connection between a similar attribute and one’s essence (Study 3) and deterring people from applying their essence to form an impression of a similar other (Study 4) — attenuated the effect of similarity on attraction. We discuss the implications for research on the self, similarity-attraction, and intergroup phenomena.