PurposeBased on the social role theory, role congruity theory and gender role conflict theory, this paper aims to investigate the mediating role of “relationship conflict” in the association between traditional gender role (TGR) endorsement and objective and subjective negotiation outcomes.Design/methodology/approachTwo experimental negotiation studies (n1 = 138, n2 = 128) were conducted at a US university.FindingsThis paper presents three original and noteworthy findings: One, in mixed-gender negotiations, as a dyad’s TGR endorsement increases, final agreements become significantly more likely to favor men than women. Two, in mixed-gender negotiations, TGR endorsement is significantly associated with a decreased ability to establish a pleasant, mutually satisfactory and successful business relationship, resulting in a possible future economic cost due to lost opportunity. Three, the heightened relationship conflict during the negotiation mediates the negative association between TGR endorsement and women’s economic outcomes.Research limitations/implicationsEmpirical findings support social role theory, role congruity theory and gender role conflict theory. The use of a distributive negotiation case and laboratory research methodology may limit the generalizability of findings.Practical implicationsFindings about the detrimental effects of TGR in mixed-gender negotiations magnify the importance of becoming aware of our TGR orientations and their potential negative consequences on our long-term collaborations. Also, it is necessary to provide negotiation trainings to both genders with regard to gender-driven conflicts and offer tools to prevent or tackle such conflicts.Social implicationsNegotiations are among the most consequential of social interactions as their results have a substantial impact on individuals’ careers and financial outcomes. Understanding the effect of TGRs is paramount to improve female representation, participation and effectiveness in management and leadership. Mixed-gender negotiations such as collective equality bargaining, workplace social interactions, work-life balance discourse are critical to establishing gender equality and fairness in organizations and societies.Originality/valueUnderstanding how gender influences negotiation processes and outcomes and using the findings to improve both genders’ negotiation success are crucial to establishing fairness and equity in society and business. This research attempts to close a gap in the literature by focusing on the potential function of gender role orientation in explaining gender differences in negotiation.