Plant-derived protein composite film is one of the promising substitutes for non-renewable petroleum-based materials. However, its application is greatly limited due to the low mechanical strength and poor antibacterial activity. In this paper, a dual network strategy based on supramolecular chemistry was reported for fabricating a high-strength and antibacterial soybean protein (SP)-based biofilm by incorporating waterborne polyurethane (WP) and quaternized chitosan (QCS). Specifically, castor oil as a renewable plant resource was used for the preparation of functional WP polymer. Based on the synergistic effect of WP network and SP network, the performance of SP-based composite film was significantly enhanced. Compared with the original SP film, the tensile strength and toughness of SP/WP/QCS film were substantially increased by 159% and 531%, respectively. In addition, the composite film showed significantly enhanced water resistance and UV shielding capability. Due to the antibacterial effect of the quaternary ammonium salt component, the SP/WP/QCS composite film exhibited superior antibacterial properties. Therefore, this study provides a feasible strategy for the preparation of high-performance SP-based films, which is expected to be applied in packaging, multifunctional adhesive, and UV-shielding coating.