A method for fabricating microvascular networks in fiber-reinforced composites is presented. The method relies on sacrificial fibers woven into fiber preforms that, when removed by depolymerization and volatilization, create 3D microvascular networks inside the composite material. By circulation of functional liquids in the resulting channels, a diverse set of new functionality is demonstrated. Simplicity, robustness, scalability, and reliance on readily available components make this method compatible with composite manufacturing methods.