This study applied a microlevel perspective on how within-individual differences in motivational and social-cognitive factors affected the weekly fluctuations of engagement in proactive career behaviors among a group of 67 German university students. Career self-efficacy beliefs, perceived career barriers, experienced social career support, positive and negative emotions, and career engagement were assessed weekly for 13 consecutive weeks. Hierarchical linear regression analyses showed that above average levels of career engagement within individuals were predicted by higher than average perceived social support and positive emotions during a given week. Conversely, within-individual differences in self-efficacy, barriers, and negative emotions had no effect. The results suggest that career interventions should provide boosts in social support and positive emotions.