Although many negotiations affect external parties, prior research has often overlooked how negotiated agreements shape the outcomes of those who are dependent on–but absent from–the bargaining table. Across one scenario and three interactive, face-to-face negotiation experiments (N = 458), we investigated how, when and why negotiators consider the outcomes of external parties. Using a novel experimental paradigm, we introduced the proximity effect–the tendency for negotiators to achieve higher joint outcomes with their direct counterparts than for affected external parties. Experiments 1 and 2 provided consistent evidence for this effect, even though improving outcomes for external parties did not come at a cost to negotiators’ own joint gains. Experiment 3 showed that the proximity effect was moderated by the interdependence structure: It disappeared under positive interdependence but persisted under negative interdependence. In Experiment 4, prompting an interdependence mindset reduced the proximity effect and improved outcomes for all involved parties. An internal meta-analysis confirmed the robustness of these findings, offering theoretical and practical insights for future research on negotiations affecting external parties.