The Everwood actress will play a Supreme Court Justice in multiple episodes, reports TVLine.
Scandal stars Kerry Washington as a former White House Communications Director who starts her own crisis management firm.
Mooney previously appeared in another Shonda Rhimes-created series. She played Owen Hunt's (Kevin McKidd) mother on Grey's Anatomy.
Meanwhile, another actor who appeared on Grey's Anatomy is also joining Scandal. Steven Bailey, who plays the bartender on the medical drama, also will be featured in season two of the political series.
Season two of Scandal will premiere on Thursday, September 27 at 10pm ET on ABC.
Watch a promo for Scandal's second season below: