Dietary mono-unsaturated fatty acids (MUFAs) are linked to human longevity and extend lifespan in several species1-12. But the mechanisms by which MUFAs promote longevity remain unclear. Here we show that an organelle hub involving lipid droplets and peroxisomes is critical for lifespan extension by MUFAs in C. elegans. MUFA accumulation increases lipid droplet number in fat storage tissues, and lipid droplet synthesis is necessary for MUFA-mediated longevity. Interestingly, the number of lipid droplets in young individuals can predict their remaining lifespan. MUFA accumulation also increases the number of peroxisomes, and peroxisome activity is required for MUFA-mediated longevity. By performing a targeted screen, we uncover a functional network between lipid droplets and peroxisomes in longevity. Interestingly, our screen also identifies ether lipids as critical components of the lipid droplet-peroxisome network. Using lipidomics, we find that the ratio of MUFAs to polyunsaturated fatty acids (PUFAs) in ether lipids is increased by MUFA accumulation. Ether lipids are involved in ferroptosis, a non-apoptotic form of cell death13-17, and MUFAs promote longevity in part via suppression of ferroptosis. Our results identify a mechanism of action for MUFAs to extend lifespan and uncover an organelle network involved in the homeostasis of MUFA-rich ether lipids. Our work also opens new avenues for lipid-based interventions to delay aging.