Social justice has become an intrinsic feature of sustainable development. One of the ways in which it is expected we will reach more just and sustainable societies is through stakeholder participation in natural resource management. However, entrenched inequalities among participants have generated scepticism about the potential of participation to improve social justice and, until now, the literature has not provided sufficient evidence to disentangle such contradictory views. Approaching social justice from the viewpoint of equality, this dissertation contributes to the debate by studying how the socio-political structure in which participation is embedded affects how far participation outcomes respect equality. The political regime, the distribution of power at the local level, and the characteristics of the participatory process are conceived as embodiments of such socio-political structure. The impact of these three structural factors on outcome equality is studied in biosphere reserves, areas designated by UNESCO as sites for experimenting with sustainable development strategies through stakeholder participation. Survey panel data from biosphere reserve managers and interview data with stakeholders are used in large-n, medium-n, and small-n analyses to explore to what extent, and under which circumstances, participation can lead to equal outcomes. The results suggest that, although in nondemocratic states participation has more difficulty promoting equal outcomes than in democratic states, and that although participation leads to generally unequal outcomes in unequal contexts, some participation outcomes can approach an egalitarian ideal even in these unexpected settings. The results suggest as well that inclusiveness and moderate empowerment of participants can contribute to equal outcomes. In short, participation has the potential to contribute to equality, but such potential varies across outcomes, contexts, and processes.