<p>Near-infrared (NIR) light-responsive shape memory polymers (SMPs) show great promise for biomedical applications, but conventional photothermal agents suffer from high cost, complex preparation, or poor biocompatibility, while lignin-based alternatives exhibit insufficient photothermal conversion efficiency. Herein, we developed a novel strategy to enhance photothermal performance of lignin through sequential demethylation modification and Fe³⁺ complexation for constructing NIR light responsive SMPs. Dealkaline lignin (DL) was first demethylated using iodocyclohexane to produce demethylated lignin (DDL) with increased catechol content, which was then incorporated into polycaprolactone-based polyurethane synthesis followed by Fe³⁺ complexation. Results showed that DDL-Fe³⁺ complexes have significantly enhanced photothermal conversion performance, and the resulting PU-DDL+Fe³⁺ polyurethane with 0.5 wt% DDL content demonstrated a temperature increases of 39.8 °C under 0.33 W·cm⁻² 808 nm NIR irradiation. This excellent photothermal performance enables the shape-fixed PU-DDL+Fe³⁺ polyurethane to rapidly recover to its initial shape under NIR light irradiation. Additionally, PU-DDL+Fe³⁺ polyurethane exhibits good mechanical properties and biocompatibility, demonstrating significant biomedical application potential.</p>