Social psychologists have developed influential theoretical models to understand intergroup conflicts, radicalism, and collective action. November 2018 saw the emergence of a new powerful movement in France named the Yellow Vests. Born on social media, the movement has sustained an unprecedented period of intense protests and violent clashes with the police, challenging the French government. As such, this movement offers an ideal context to examine the real‐world relevance of current social‐psychological theorizing. Using a social identity and self‐categorization perspective, two correlational studies (three samples, N = 1,849) tested the role of self‐categorization as a group member, or social identity, in accounting for individual participation in normative and nonnormative collective action. Using different operationalizations of identification, both studies confirm a powerful role of identification as a Yellow Vest and provided evidence that the effect of social media use on collective action is fully mediated by self‐categorization as a Yellow Vest. An alternative model suggesting that social media use mediated the relation between social identity and collective action was not supported by the data.