Lignin‐grafted copolymers, namely lignin‐graft‐poly(methyl methacrylate‐co‐butyl acrylate) (lignin‐g‐P(MMA‐co‐BA)), are synthesized via “grafting from” atom transfer radical polymerization (ATRP) with the aid of lignin‐based macroinitiators. By manipulating the monomer feed ratios of MMA/BA, grafted copolymers with tunable glass transition temperatures (−10–40 °C) are obtained. These copolymers are evaluated as sustainable thermoplastic elastomers (TPEs). The results suggest that the mechanical properties of these TPEs lignin‐g‐P(MMA‐co‐BA) copolymers are improved significantly by comparing with those of linear P(MMA‐co‐BA) copolymer counterparts, and the elastic strain recovery is nearly 70%. Lignin‐g‐P(MMA‐co‐BA) copolymers exhibit high absorption in the range of the UV spectrum, which might allow for applications in UV‐blocking coatings.