The present research investigated the associations of collectivism with lay theory of generalized prejudice (LTGP) endorsement and, consequently, intraminority allyship. Study 1 recruited people from Chile, Germany, Mexico, Israel, and the United States ( N = 655) and found that higher levels of self-reported collectivism were associated with stronger LTGP endorsements. Study 2 replicated this collectivism-LTGP relationship among Chinese individuals in 19 countries ( N = 118). In Study 3, Latinx U.S. participants ( N = 334) primed with high (versus low) collectivism endorsed LTGP more strongly, which was associated with greater stigma-based solidarity and intraminority allyship. Study 4 recruited from Greece, South Africa, Mexico, New Zealand, and the United States ( N = 778), and found that horizontal (but not vertical) collectivism was associated with LTGP and thus allyship. Study 4 identified three mechanisms linking (horizontal) collectivism and LTGP: connecting discrimination, attention to discrimination, and empathy. Findings highlight collectivistic mindsets as a strategy to facilitate intraminority coalitions.