Article 3 of the U.S. Constitution states that Justices "shall hold their Offices during good Behaviour." The term "good behavior" is understood to mean justices may serve for the remainder of their lives, unless they are impeached and convicted by Congress, resign or retire.

Note from history: The only Justice to be impeached was Associate Justice Samuel Chase in 1805.

This might be interesting: Samuel Chase was born on the 17th of April, 1741.His political views changed over his lifetime. In the last decades of his career, he became well known as a staunch Federalist. He was impeached on grounds of letting his partisan leanings affect his court decisions.

More Info: en.wikipedia.org