Conservation interventions are central strategies for achieving sustainable development goals given the inextricable dependence of humanity on nature. Current debate centres on whether interventions such as marine protected areas (MPAs) promote co-benefits or trade-offs among multiple goals such as poverty alleviation, food security and protection of marine resources. Resolving this question is hindered by a lack of quantitative impact evaluations of concurrent ecological and social co-benefits of MPAs. Here we use a statistical matching approach to examine whether MPAs are associated with co-benefits or trade-offs between reef fish abundances and measures of human well-being, including income, diet and food security in the Mesoamerican region. We find that highly protected areas (HPAs) with stringent fishing restrictions tend to support high mean abundances and stable or increasing trends in fish abundances compared with unprotected sites and ‘general use zones’ of MPAs. At the same time, indicators of income and food security were elevated in communities near MPAs, especially HPAs, compared with communities far from MPAs. Finally, proximity to MPAs and to reefs with high fish abundance were both positively associated with well-being across space. Together, these results provide quantitative evidence of co-benefits for fish and people associated with MPAs, highlighting the potential value of MPAs in achieving multiple sustainable development goals.