Herein, antibacterial bioplastic derived from lignin, poly(butylene succinate-co-butylene terephthalate) (PBST) was functionalized with the antibacterial lignin-g– (polyhexamethylene guanidine) (Lignin-g-PHMG). The Lignin-g-PHMG was synthesized by a facile grafting reaction. The epoxidized lignin provided sufficient reactive sites for the amine groups on PHMG. The structure of Lignin-g-PHMG was confirmed by Fourier-Transform Infrared Spectra (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). The antibacterial bioplastics were developed by introducing Lignin-g-PHMG into the matrix of PBST and lignin. The composite bioplastics exhibited good mechanical performance, with a tensile strength of 20.69 MPa and an elongation at break of 414.88%, respectively. Moreover, the composite films revealed good antioxidant properties, and a highly efficient scavenging rate of 98.21% was detected for DPPH free radicals. The bacterial inhibition by the bioplastic composite films demonstrated a synergistic antibacterial effect between lignin and Lignin-g-PHMG on E. coli and S. aureus. Furthermore, the inhibition zone test indicated that the bioplastic composite could provide a durable and nonleaching antibacterial performance. Therefore, this study contributes to the conversion of lignin into multifunctional composites with potential antioxidant and antimicrobial applications.