Expressive accuracy, being viewed in line with one’s unique, distinctive personality traits, is emerging as a fundamental individual difference that is strongly linked to psychological well-being. Yet little is known about what underlies expressive accuracy and its associations with well-being. The current studies examined whether personality-behavior congruence, the tendency to behave in line with one’s distinctive personality trait profile, contributes to the links between well-being and expressive accuracy with new acquaintances (Unique perceiver-target pairs: Study 1: N = 437; Study 2: N = 874), by assessing congruence in a range of naturalistic situations, including in a series of getting-acquainted interactions (Study 1; Ntargets = 77; Mdn Interactions: 7) and social situations in daily life over a two-week period (Study 2; Ntargets = 146; MdnAssessments: 49). Across studies, we found that greater well-being predicted greater congruence, in both naturalistic social interactions and in daily life, which in turn contributed to greater expressive accuracy in getting-acquainted interactions. Overall, the current studies demonstrate the important role that congruence plays in expressive accuracy, helping to explain why well-adjusted individuals are seen more accurately.