It is vital to unveil the effects of extracellular matrix cues on endothelial cell (EC) outgrowth for desirably governing vasculature formation, but the role of matrix plasticity on EC outgrowth is elusive. Here, the authors develop hydrogels with tunable mechanical plasticity independent of stiffness, and elucidate the plasticity-mediated responses of ECs during vasculogenesis and angiogenesis.