All interactions between multiple species invading together (coinvasion) must be accounted for to predict species coexistence patterns across space. Mutualisms, particularly, are known to influence species' population dynamics and their invasive ability (e.g., mycorrhizal fungi with partner plants). Yet, while modeling coinvasion, their role in mediating coexistence is overlooked. Here, we build a spatially explicit model of coinvasion of two competing plant species with a shared fungal mutualist to study how mutualism and competition interact to shape the local and regional coexistence of competitors. We observe four main results. First, mutualist presence generates regional coexistence between competitors even when local coexistence between them is impossible. Second, increasing partner mutualist dispersal leads to abrupt changes in competitor coexistence outcomes. Third, differences in mutualist partner dependence and competitive ability interact to produce a variety of local and regional coexistence outcomes. Fourth, asymmetry in the dispersal ability arising from dependence-dispersal trade-offs leads to greater exclusion of species less dependent on mutualist partners for growth. In toto, incorporating mutualism-specific trait trade-offs and dispersal asymmetries into coinvasion models offers new insights into regional coexistence and invasive species distributions.