Upward influencers, employees who are more favorably perceived by their supervisors than their peers and subordinates, are predicted by economic and accounting theories and are found to be ubiquitous in many organizations. Despite their prevalence, the role of upward influencers in teams remains underexplored. This paper fills this void by using proprietary data from a service‐providing organization that allows for the identification of upward influencers based on its 360‐degree person evaluation. We find an inverted U‐shaped relationship between the fraction of upward influencers in a team and team performance. In cross‐sectional analyses, we show that this relationship is driven by conditions when the need for collaboration and information sharing is high and when managers are less experienced. Additional tests exploring the mechanisms for the role of upward influencers in teams suggest that they impair team horizontal relationships through lowering the willingness to communicate, share knowledge, and offer mutual assistance among team members. Yet, teams with upward influencers build better vertical relationships with supervisors, which, in return, is associated with supervisors allocating more of their time to provide team members with feedback and guidance. Taken together, this study contributes to the understanding of upward influencers in teams.