McDermott, best known for his role on ABC’s long-running drama The Practice, will star alongside Christopher Meloni in the NBC drama.
The network didn’t say who McDermott would play in the SVU spin-off, which is set to premiere later this year.
It comes after production started earlier this week with Meloni and Mariska Hargitay shared a photo on set.
Meloni is reprising his role as Elliot Stabler, who returns to the NYPD to battle organized crime after a devastating personal loss. Stabler will aim to rebuild his life as part of a new elite task force that is taking apart the city’s most powerful criminal syndicates one by one.
Law & Order: Organized Crime was created by Dick Wolf, who will executive produce along with Ilene Chaiken, Terry Miller, Fred Berner, Arthur W. Forney and Peter Jankowski.
The series is produced by Wolf Entertainment and Universal Television, a division of Universal Studio Group.
McDermott is repped by Industry Entertainment and CAA.