The Poppy Montgomery-fronted drama also has added a pair of recurring players for its sophomore run, which kicks off July 28.
Per our sister site Deadline, Roberts will play Eliot, the new boss of the Major Cases Section of the NYPD.
On the recurring front, Tawny Cypress (Heroes, House of Cards) has been cast as Murray, a decorated FBI agent who begins work at the Major Cases Section, while James Liao (Prison Break) will play Jay, a detective with expertise in a wide range of technical subjects.
As previously reported, while Montgomery, Dylan Walsh and Jane Curtin are returning as regulars, Michael Gaston (The Mentalist), Kevin Rankin (Justified) and Daya Vaidya — who played Detectives Mike Costello, Roe Saunders and Nina Inara — are no longer a part of the full-time cast.
Production on Unforgettable will commence sometime after Montgomery gives birth to her second child, this spring.