How do perceivers build up social category knowledge from the face, and then act on it? I investigated this using event-related potentials. In Study 1, participants made between-hand sex-categorizations of sex-typical and sex-atypical faces. Sex-atypical faces evoked larger N300/N400 effects, reflecting the integration of accumulating sex-category knowledge into a coherent interpretation. Sex-atypical faces also induced a parallel competition between sex-categories, as revealed by the lateralized readiness potential (LRP). Additionally, the LRP revealed that motor cortex began preparing for action while social category knowledge was still gradually evolving in parallel. Lastly, sex-typical faces evoked an enlarged N170, reflecting visual sex-category encoding. In Study 2, participants made between-hand eye-color categorizations as part of go/no-go trials that were contingent on target sex. On no-go trials, information about eye color partially prepared motor cortex to move the hand before face perception had been finalized. Together, these findings demonstrate the continuous dynamics in person construal. Face perception continuously flows into action.