When did the two term presidency rule go into effect?
Twenty-second Amendment to the United States Constitution
February 27, 1951
Prior to the ratification of the amendment, the president had not been subject to term limits, but George Washington had established a two-term tradition that many other presidents had followed. In the 1940 presidential election, Franklin D. Roosevelt became the first president to win a third term, giving rise to concerns about the potential issues involved with a president serving an unlimited number of terms. Congress approved the Twenty-second Amendment on March 24, 1947, and submitted it to the state legislatures for ratification. That process was completed on February 27, 1951, after the amendment had been ratified by the requisite 36 of the then-48 states (as neither Alaska nor Hawaii had yet been admitted as states), and its provisions came into force on that date.