The cop drama will star Warren Kole and Michael Ealy as two bickering homicide detectives who are sent to couples' counselling.
Former Lost star Walger will play the pair's quick-witted psychiatrist, according to Entertainment Weekly.
Tired of treating her rich clientele from a Beverly Hills practice, Walger's character begins offering low-cost therapy at a local community centre.
The actress played Penny on Lost between 2006 and 2010 and later starred in ABC's FlashForward.
She has also appeared on HBO's In Treatment, Fox's Terminator: The Sarah Connor Chronicles and CBS series CSI: NY
Common Law begins shooting next month in New Orleans and will premiere in 2012 on USA.
> Jack McGee lands Common Law role
> Amy Acker joins Common Law pilot