Curtis will reunite with his former boss, Lt. Anita van Buren (S. Epatha Merkerson), on an upcoming episode. Bratt was nominated for a best supporting actor Emmy for the role in 1999. After four seasons, he left the show that same year to pursue a film career.
"I am thrilled that Ben is coming back for a return appearance," executive producer Dick Wolf said in a statement. "He joined us for our recent 20th anniversary celebration and it was like he never left."
Bratt's casting was first reported by Entertainment Weekly's Michael Ausiello.
Bratt starred in the A&E series The Cleaner for two seasons and will guest-star this fall on ABC's hit sitcom Modern Family, playing Sofia Vergara's unreliable but charismatic ex-husband.