An associate justice of the Supreme Court of the United States is any member of the Supreme Court of the United States other than the chief justice of the United States. The number of associate justices is eight, as set by the Judiciary Act of 1869.Article II, Section 2, Clause 2 of the Constitution of the United States grants plenary power to the president to nominate, and with the advice and consent (confirmation) of the Senate, appoint justices to the Supreme Court. Article III, Section 1 of the Constitution effectively grants life tenure to associate justices, and all other federal judges, which ends only when a justice dies, retires, resigns, or is removed from office by impeachment.Each Supreme Court justice has a single vote in deciding the cases argued before it, and the chief justice's vote counts no more than that of any other justice; however, the chief justice leads the discussion of the case among the justices. Furthermore, the chief justicewhen in the majoritydecides who writes the court's opinion; otherwise, the senior justice in the majority assigns the writing of a decision. The chief justice also has certain administrative responsibilities that the other justices do not and is paid slightly more ($286,700 per year as of 2022, compared to $274,200 per year for an associate justice).Associate justices have seniority in order of the date their respective commissions bear, although the chief justice is always considered to be the most senior justice. If two justices are commissioned on the same day, the elder is designated the senior justice of the two. Currently, the senior associate justice is Clarence Thomas. By tradition, when the justices are in conference deliberating the outcome of cases before the Supreme Court, the justices state their views in order of seniority. The senior associate justice is also tasked with carrying out the chief justice's duties when he is unable to, or if that office is vacant. Historically, associate justices were styled "Mr. Justice" in court opinions and other writings. The title was shortened to "Justice" in 1980, a year before Sandra Day O'Connor became the first female justice.

Thurgood Marshall (July 2, 1908 – January 24, 1993) was an American lawyer and civil rights activist who served as Associate Justice of the Supreme Court of the United States from October 1967 until October 1991. Marshall was the Court's first African-American justice. Prior to his judicial service, he successfully argued several cases before the Supreme Court, including Brown v. Board of Education.

Born in Baltimore, Maryland, Marshall graduated from the Howard University School of Law in 1933. He established a private legal practice in Baltimore before founding the NAACP Legal Defense and Educational Fund, where he served as executive director. In that position, he argued several cases before the Supreme Court, including Smith v. Allwright, Shelley v. Kraemer, and Brown v. Board of Education, the latter of which held that racial segregation in public education is a violation of the Equal Protection Clause.

In 1961, President John F. Kennedy appointed Marshall to the United States Court of Appeals for the Second Circuit. Four years later, President Lyndon B. Johnson appointed Marshall as the United States Solicitor General. In 1967, Johnson successfully nominated Marshall to succeed retiring Associate Justice Tom C. Clark as an Associate Justice of the Supreme Court of the United States. Marshall retired during the administration of President George H. W. Bush in 1991, and was succeeded by Clarence Thomas.