Integrating theorizing across the mindfulness and negotiation literatures, we hypothesize that mindfulness increases cooperation in negotiations. We further propose that processes of self-transcendence, self-regulation, and self-awareness mediate this effect. We test these hypotheses in five studies across different forms of cooperation, in both distributive and integrative negotiation contexts, and for both measured and experimentally induced mindfulness. In Study 1a, individuals higher on measured state mindfulness displayed greater cooperative orientation measured as preference for pareto-optimal agreements. In Study 1b, experimentally induced mindfulness led to greater cooperative orientation measured as the recall of cooperative heuristics. In Study 2, a distributive (fixed-sum) negotiation, dyads who engaged in a mindfulness practice before the negotiation were more likely to reach cooperative agreements with more equal distribution of the bargaining zone than control condition dyads. In Study 3, an integrative negotiation, dyads who engaged in a mindfulness practice before the negotiation were more likely to reach win–win agreements than control condition dyads. Finally, in Study 4, another integrative negotiation, we found that mindful dyads achieved greater joint gains and the effect was mediated by self-transcendence. Overall, results provide substantial evidence that mindfulness is an effective intervention for increasing cooperation in negotiations.