This research aimed to enhance understanding of how relationships among trait affect and individual performance are influenced by group affective properties. To do this, we integrated trait affect and affective diversity theories within a self-regulatory framework to generate predictions regarding the moderating effect of group trait affect and group affective diversity on the relationship between trait affect and individual performance. Hypotheses were tested in groups working for 6-months on industry-relevant thesis projects. Trait affect was collected on Day 1 of the course. Group trait affect was operationalized as mean level of trait affect within each group. Group affective diversity was operationalized as the standard deviation of trait affect within each group. Individual performance was measured via peer-ratings of work-role proficiency and supervisor-rated thesis grades. The detrimental effect of trait negative affect on individual performance was buffered for individuals who were working with affectively similar peers – groups characterized by high group trait negative affect and low group negative affective diversity. Further, the beneficial effect of group trait positive affect on individual performance was strengthened when group positive affective diversity was low. Our findings highlight the importance of considering multiple affective properties at both individual and group levels in order to understand affective influences on individual performance.