The actor will join Skeet Ulrich on the spinoff, playing TJ Jaruszalski, the partner of Ulrich's Detective Rex Winters.
Deadline describes Jaruszalski as "a confident Hollywood native with a cynical view of the entertainment industry". The character will also reportedly be portrayed as "a health nut with an active social life".
Stoll starred in a 2006 episode of the original Law & Order series, and also appears in new Angelina Jolie film Salt.
Spider-Man 2 star Alfred Molina was previously cast as deputy district attorney Peter Morales in the series.
Law & Order: Los Angeles premieres on NBC on September 22.