The low fracture toughness of oxide glasses is a key limitation for many of their applications. Inducing and controlling nanoscale phase separation in oxide glasses has been proposed as a potential toughening strategy, as, unlike many alternative extrinsic toughening approaches, it allows one to retain the optical transparency. Using molecular dynamics simulations, we here investigate the toughening mechanism in soda-lime-silica glasses with embedded glassy nanoscale silica droplets. This system is chosen as a model for the experimental structure of phase-separated soda-lime-silica glass, which is attractive considering its existing commercial use and the ease of inducing phase separation. We calculate the fracture toughness of glass structures containing nanodroplets of varying sizes and with different precrack positions, revealing that the glassy silica droplets toughen the material. The simulations show that crack propagation is impeded by crack arrest, crack deﬂection and diversion, and stress ﬁeld alteration, ultimately increasing the fracture toughness. Our ﬁndings thus shed light on the toughening mechanism due to phase separation, with important implications for the experimental design of oxide glasses with controlled nanoscale phase separation.