Women are underrepresented in business, academic, and political decision-making bodies across the world. To investigate the causal effect of gender representation on multilateral negotiations, we experimentally manipulate the composition of triads in a majoritarian, divide-the-dollar game. We document a robust gender gap in earnings, driven largely by the exclusion of women from alliances rather than differential shares within alliances. Experiments with different subject pools show that distinct bargaining dynamics can underlie the same inequitable outcomes: While gender-biased outcomes can be caused by outright discrimination, they can also be driven by more complex dynamics related to differences in bargaining strategies. We identify two fundamental gender differences in bargaining dynamics. First, men are more likely to make opening offers and enjoy a payoff advantage for doing so, yet women that propose first do not and may even suffer backlash. Second, mixed-gender alliances are less stable when the excluded party is male rather than female. These findings show that there is no "one-size-fits-all'' solution to the gender gap we uncovered and highlight the importance of studying bargaining dynamics in detail.