At low temperatures, monolithic bulk metallic glasses (BMGs) exhibit high strength and large elasticity limits. On the other hand, BMGs lack overall ductility due to highly localized deformation mechanisms. Recent experimental findings suggest that the problem of catastrophic failure by shear band propagation in BMGs can be mitigated by tailoring microstructural features at different length scales to promote more homogeneous plastic deformation. Herein, based on a continuum approach, we present a quantitative analysis of the effects of microstructure on the deformation behavior of monolithic BMGs and BMG composites. In particular, simulations highlight the importance of short-ranged structural correlations on ductility in monolithic BMGs and demonstrate that particle size controls the ductility of BMG composites. In broader terms, our results provide new avenues for further improvements to the mechanical properties of BMGs.