Abstract: Objective In response to the limited research on the laser welding process of medium-thick TWIP steel, this study investigates the influence of welding speed on the microstructure and properties of 8.2 mm thick TWIP steel laser welded joints. Methods Welding trials were conducted using fiber laser butt welding at speeds of 0.5 m/min, 1 m/min, and 2 m/min. The joints were characterized by OM, SEM, EBSD, EDS, XRD, hardness testing and tensile testing. Results The results indicate that full penetration of welds was achieved at all three speeds, with welds microstructure consisting of coarse columnar austenite grains which refined as the welding speed increased. The Mn content slightly decreased in both the weld and heat-affected zone, with greater loss observed at lower speeds. The joint tensile properties first increased and then decreased with welding speed increasing, all specimen fractured in weld zone, showing ductile fracture characteristics. The optimal property was achieved at welding speed of 1 m/min, with tensile strength of 979 MPa and elongation after fracture of 49.95%, reaching 94% and 74.33% of the base material, respectively. This was attributed to fine dendrites, high fraction of substructures and low defects in the weld at this parameter. Conclusion Welding speed is identified as a key factor to affecting the laser welding quality of medium-thick TWIP steel. A welding speed of 1 m/min ensures a good balance between full penetration and strength-ductility. The findings clarify the intrinsic relationship of welding speed, microstructure and mechanical properties, providing important insights for the laser welding of medium-thick TWIP steel.