The actor's movie credits include "Get Shorty," "Midnight Run," "Out of Sight" and the upcoming "Purple Violets" and "You Kill Me."
Dick Wolf, creator and executive producer of the NBC drama, said in a statement that he respected Farina's decision and looked forward to working with him again.
Farina's departure isn't the only change for "Law & Order," which has a long history of cast turnover. Assistant District Attorney Alexandra Borgia, played by Annie Parisse, was killed in the season finale as she investigated a murder case.
Parisse was part of a succession of actresses playing young female prosecutors paired with assistant D.A. Jack McCoy (Sam Waterston), including Jill Hennessy, Carey Lowell, Angie Harmon and Elisabeth Röhm.
Farina had succeeded longtime series fixture Jerry Orbach, whose Detective Lennie Briscoe was to be featured in a "Law & Order" spinoff before Orbach's death in 2004.
There was no announcement of cast additions for next season, a "Law & Order" spokeswoman said Tuesday.