First Justice existed as a role in the judicial systems of both the Galactic Republic and the New Republic.
Within the Galactic Republic, the First Justice held the position of second-in-command to the twelve justices of the Supreme Court. Consequently, the First Justice's responsibilities encompassed any duties delegated by the Chief Justice. The First Justice also oversaw all other justices and the other Courts.
During the era of the New Republic, the First Justice served as a member of the Court of Justice, chosen by the members of the court from among themselves.