Northern Mariana Islands Legal Residents Relief Act of 2021 This bill expands eligibility for obtaining Commonwealth of the Northern Mariana Islands (CNMI) Resident status, provides a path for holders of such status to obtain U.S. permanent resident status, and makes CNMI-only transitional workers eligible to receive government relief or assistance in connection with a declared emergency. CNMI Resident status was available to qualifying individuals who applied for such status between February 19, 2020, and August 17, 2020. Among other requirements, a qualifying individual must have (1) been lawfully present in the CNMI on certain dates, and (2) continually and lawfully resided in the CNMI from November 28, 2009, through June 25, 2019. The bill reopens the period for applying for such status for 180 days and authorizes the Department of Homeland Security to waive this deadline in certain instances. The bill allows additional classes of individuals to qualify for CNMI Resident status, including an individual who (1) was admitted as a transitional worker during FY2015 and each subsequent fiscal year through FY2018, (2) is a qualified investor, or (3) resided in the CNMI as a guest worker for certain periods and is currently a transitional worker. The bill also waives the continual residence requirement for certain individuals and allows an individual lawfully present on December 31, 2020, to qualify. A qualifying alien with CNMI Resident status may obtain U.S. permanent resident status after holding CNMI Resident status for five years or after this bill has been enacted for five years, whichever is later.