In the Galactic Republic, the First Justice was the second in command of the twelve justices in the Supreme Court. As such, the First Justice was in charge of all the things the Chief Justice left behind. The First Justice also was in charge of all other justices and the other Courts.
Under the New Republic, the First Justice was a member of the Court of Justice, and was elected by the body from among their number.
- Cracken's Threat Dossier