The current research examined the interpersonal dynamics of emotion regulation in a stressful collaborative context. Little is known about how regulating one’s own stress responses impacts teammates. In this article, we propose that individual efforts to regulate emotions can impact teammates for the better. We tested hypotheses arising from this claim using a dyadic experiment ( N = 266) that assessed in vivo physiological stress responses during collaborative work (a face-to-face product design task) and then individual work (a product pitch to evaluators). Throughout the experiment, the manipulated teammate was randomly assigned to reappraise their stress arousal, suppress their emotional displays, or receive no instructions. The nonmanipulated teammate received no instructions in all experimental conditions. Stress reappraisal benefited both teammates, eliciting challenge-like physiological responses (higher cardiac output, lower total peripheral resistance) relative to the suppression and control conditions. These effects were observed during both collaborative and individual work. A mediation model suggested that face-to-face interpersonal effects of stress reappraisal fed forward to promote nonmanipulated teammates’ improved stress responses during individual performance. Moreover, manipulated teammates’ displays of positive and negative affect emerged as potential mechanisms for improvements in nonmanipulated teammates’ stress responses in moderation analyses. Thus, participants benefited by interacting with a person who reappraised their stress as functional. This work has theoretical implications for the interpersonal dynamics of emotion regulation, and relevance for applied settings is also discussed.