Final answer:
Federal judges, including Supreme Court justices, hold their offices during good behavior, which means they can serve for life.
Step-by-step explanation:
The main provision in the Constitution that outlines how long a judge is allowed to maintain his position after being appointed is found in Article III. According to this provision, federal judges, including Supreme Court justices, hold their offices during good behavior, which has come to mean they can serve for life. This provision was included to ensure the independence of the judiciary from political influence.