Lignin, as an abundant carbon-rich renewable resource, is a promising precursor for carbon fibers. However, due to the poor spinnability of lignin, a great challenge comes from the spinning of precursor fibers. In this work, a series of lignosulfonate-acrylonitrile (LS-AN) copolymers with different LS contents were prepared by a two-step process consisting of esterification and free radical copolymerization. In this strategy, lignin was used as a macromer and chemically bonded to acrylonitrile segmer, resulting in significant improvement of the spinnability. Continuous long precursor fibers with a dense structure were successfully prepared from these copolymers by a wet spinning technique and then converted into carbon fibers by thermal stabilization and carbonization. The LS-AN copolymers were characterized by FTIR, GPC, and rheological method. The results confirmed the macromolecular characteristic of the LS-AN copolymers. A hanging lantern model was proposed to describe the molecular structure of the LS-AN copolymers. Effect of the LS-AN copolymers on the microstructure and mechanical properties of carbon fibers was investigated by SEM, single fiber tensile testing, XRD, and HRTEM. The results demonstrated the feasibility of developing partially biobased carbon fibers from the novel LS-AN copolymers.