Definition of Ex Officio Justices
Judges who serve in a particular capacity by reason of their office as a judge who serves on a commission or board because the law requires a particular judge to serve thereon and not because he is selected for such post. May also refer to one who exercises judicial functions by reason of his office.
That's the definition of Ex Officio Justices in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.