Iran Diplomacy Act of 2021 This bill outlines U.S. policy with respect to Iran and the Joint Comprehensive Plan of Action (JCPOA), commonly known as the Iran nuclear deal. Specifically, the bill states that the United States and Iran should promptly return to full compliance with their commitments under the JCPOA. Further, the bill encourages the United States to lead international efforts to advance diplomatic measures that promote U.S., regional, and international security.