Climate change can alter conditions that sustain food production and availability, with cascading consequences for food security and global economies. Here, we evaluate the vulnerability of societies to the simultaneous impacts of climate change on agriculture and marine fisheries at a global scale. Under a “business-as-usual” emission scenario, ~90% of the world’s population—most of whom live in the most sensitive and least developed countries—are projected to be exposed to losses of food production in both sectors, while less than 3% would live in regions experiencing simultaneous productivity gains by 2100. Under a strong mitigation scenario comparable to achieving the Paris Agreement, most countries—including the most vulnerable and many of the largest CO2 producers—would experience concomitant net gains in agriculture and fisheries production. Reducing societies’ vulnerability to future climate impacts requires prompt mitigation actions led by major CO2 emitters coupled with strategic adaptation within and across sectors.