The actress will see her role as a take-charge nurse with a mysterious past and will continue into the previously announced fourth season when she becomes more entangled with the Lyon family, according to The Hollywood Reporter.
"Empire" will mark Moore's biggest TV role since her regular run on "General Hospital"; her small-screen credits also include episodes of "Will and Grace" and "Ellen".
The third season also stars Eva Longoria, Taye Diggs, Phylicia Rashad, Nia Long and Moore's daughter, Rumer Willis.