Although there is robust evidence that being more extraverted is related to higher popularity, only few studies have examined which actual behaviours (e.g., verbal content, body language) might explain this association. The current study examined whether observer-rated dominant behaviours (nonverbal, paraverbal, verbal, and general cues) mediate the relationship between self-rated extraversion and its facets (assertiveness, sociability, and activity) and other-rated popularity in zero-acquaintance settings. In two studies, we analysed data from face-to-face (Study 1, N = 124) and virtual (Study 2, N = 291) group interactions where participants were videotaped while performing a task and subsequently rated each other on popularity. Across studies, extraversion and the facets assertiveness and sociability were consistently associated with higher popularity, while the role of dominant behaviours differed. In Study 1, only two nonverbal behaviours, dominant gestures and upright posture, mediated the association between extraversion and popularity. In Study 2, all four types of behavioural cues mediated the association between extraversion (facets) and popularity. We discuss how these findings provide insights into the mechanisms of attaining popularity at zero acquaintance in diverse social settings.