Medicare for All Act of 2021 This bill establishes a national health insurance program that is administered by the Department of Health and Human Services (HHS). Among other requirements, the program must (1) cover all U.S. residents; (2) provide for automatic enrollment of individuals upon birth or residency in the United States; and (3) cover items and services that are medically necessary or appropriate to maintain health or to diagnose, treat, or rehabilitate a health condition, including hospital services, prescription drugs, mental health and substance abuse treatment, dental and vision services, and long-term care. The bill prohibits cost-sharing (e.g., deductibles, coinsurance, and copayments) and other charges for covered services. Additionally, private health insurers and employers may only offer coverage that is supplemental to, and not duplicative of, benefits provided under the program. Health insurance exchanges and specified federal health programs terminate upon program implementation. However, the program does not affect coverage provided through the Department of Veterans Affairs or the Indian Health Service. The bill also establishes a series of implementing provisions relating to (1) health care provider participation; (2) HHS administration; and (3) payments and costs, including the requirement that HHS negotiate prices for prescription drugs. Individuals who are age 18 or younger, age 55 or older, or already enrolled in Medicare may enroll in the program starting one year after enactment of this bill; other individuals may buy into the program at this time. The program must be fully implemented two years after enactment.