Keratin, a valuable protein obtained from chicken feather waste from the food industry, was used in this study in combination with a biobased formulation of epoxidized linseed oil (ELO) and dodecenylsuccinic anhydride (DDSA). The influence of keratin on the ELO cross-linking reaction was studied using differential scanning calorimetry (DSC) and in situ Fourier transform infrared (FT-IR) spectroscopy, showing the chemical contribution of the protein during network formation. Moreover, keratin showed a positive effect on the overall performances of the network, glass transition, storage modulus, and tensile strength, proving its potential in developing sustainable materials with industrial application potential.