Mary Kay O'Brien is a judge for the 3rd District of the Illinois Supreme Court. She assumed office on December 5, 2022. Her current term ends on December 6, 2032. O'Brien ran for election for the 3rd District judge of the Illinois Supreme Court. She won in the general election on November 8, 2022. O'Brien was a judge of the Illinois Third District Appellate Court from 2003 to 2022.