The incorporation of proteins into hydrogel networks has the potential to enhance bioactivity and biocompatibility. In this work, we report on the fabrication of a polymer-protein hydrogel consisting of polymethacrylamide (PMAAm) and bovine serum albumin (BSA). The hydrogel was prepared by in situ polymerization of methacrylamide in the presence of BSA at elevated temperatures. Due to its specific interactions between corresponding functional groups, BSA acts as a cross-linker of polymer chains. Hydrogel with optimized composition and preparation conditions (BSA/methacrylamide ratio and synthesis temperature) demonstrated excellent mechanical properties. Due to the presence of side amide groups in PMAAm, the energy barrier required for heat-induced transformation of globular BSA structures into unfolded linear structures decreased, causing a significant shift in the transition temperature. This transition led to a steep and substantial strengthening of the two-component hydrogel. After compressive and shear deformation, the hydrogel restored damaged structure and demonstrated superior fatigue resistance. Compared to BSA that is globular, it was found that BSA in its unfolded state has a much greater impact on the mechanical properties of the hydrogel.