Smart Manufacturing Leadership Act of 2021 This bill addresses the productivity and energy efficiency of the manufacturing sector as well as the development of smart manufacturing technologies (certain advanced technologies in information, automation, monitoring, computation, sensing, modeling, and networking). Specifically, the Department of Energy (DOE) may make grants to states for supporting the implementation of smart manufacturing technologies. States must use those grants to (1) provide access to shared supercomputing facilities to small- and medium-sized manufacturers, (2) fund research and development of transformational manufacturing processes and materials technology that advance smart manufacturing, and (3) provide tools and training to aid the adoption of energy management systems and implement smart manufacturing technologies in the manufacturers' facilities. In addition, DOE must expand the scope of technologies covered by its Industrial Assessment Centers to (1) include smart manufacturing technologies and practices, and (2) equip the centers' directors with the training and tools necessary to provide technical assistance in smart manufacturing technologies and practices. DOE must also (1) study how it can increase access to existing high-performance computing resources in its National Laboratories, and (2) facilitate access to the laboratories by small- and medium-sized manufacturers.