•A approach of reinforcing metals using a three-dimensional metallic glass lattice was developed.•Novel metal matrix composites with excellent mechanical properties were prepared.•The enhanced mechanical properties mainly originate from mutual-reinforcement mechanism and well-designed structure.•Yield strengths of the novel composites are strongly dependent on the structure of metallic glass lattices. Although various methods have been developed to manufacture metal matrix composites (MMCs), most of the currently employed methods use discontinued crystalline ceramic particles as reinforcements. Herein, we report a new approach of reinforcing metals using a three-dimensional metallic glass (MG) lattice. Specifically, the processing route involves additive manufacturing of a stainless-steel matrix scaffold containing a continuous lattice-structured cavity and subsequent high-pressure injection of a Zr-based glass-forming liquid into the scaffold. Our results demonstrate that the as-produced composites reinforced with 30 vol% MG in the form of a body-centered-cubic lattice possess excellent mechanical properties. Remarkably, the plasticity is higher than those of some particle-reinforced stainless-steel composites and most conventional ex situ MG matrix composites. The enhanced performances mainly arise from the well-designed structure, good combination of the hard MG and soft stainless steel, and their mutual reinforcement mechanism. This study not only reveals a new class of composites reinforced with lattice-structured MG that overcome the limitation of MG reinforcement, rendering it suitable for reinforcing high-melting-point materials, but also provides a novel design concept and fabrication approach that could be extended to other alloy systems for achieving improved mechanical properties. Display omitted