Many employees in today’s organizations are involved in more than one team at the same time. Building on the challenge‐hindrance stressor framework, this study investigates potential benefits and disadvantages of such multiple team membership (MTM) for individual employees. Furthermore, we extend this framework with insights from the job demands‐resources model to propose that, depending on an employee’s organizational tenure, individual MTM will differentially shape his or her perceptions of work challenge and role ambiguity, subsequently influencing the employee’s job performance and absenteeism. We tested our conceptual model using time‐lagged multi‐source data from a large organization of applied research (N = 1211). Our results demonstrate that, for employees with relatively low organizational tenure, MTM was negatively associated with perceived work challenge and positively associated with perceived role ambiguity, which in turn associated with lower job performance and higher absenteeism. For employees with higher organizational tenure, by contrast, MTM associated positively with their work challenge perceptions and subsequent performance outcomes, whereas MTM was unrelated to perceived role ambiguity as well as absenteeism. These findings identify relevant psychological mechanisms and a key contingency factor that explain when and why MTM may have positive or negative individual‐level consequences.