Grandiose narcissism has been linked to initial popularity but to later unpopularity in peer groups and laboratory contexts. Do these effects on peer relationships also emerge in larger real-life contexts and what are the underlying behavioral processes (i.e., behavioral expressions, interpersonal perceptions)? Using data from the longitudinal CONNECT field study (N = 126), we investigated effects of agentic and antagonistic aspects of grandiose narcissism on emerging popularity in a complete peer network. A cohort of psychology first-year students was assessed with a quasiexperimental, experience-sampling methodology involving online surveys, diaries, and behavioral observations. In contrast to previous laboratory research, narcissism was unrelated to popularity at the level of zero-order correlations. However, results indicated that (a) an agentic behavioral pathway fostered popularity across time, and an antagonistic behavioral pathway drove the long-term decline in popularity, and (b) the two pathways were differentially related to agentic (admiration) and antagonistic (rivalry) aspects of narcissism.