The comedy-drama, which was picked up for 11 episodes in July, stars Michael Ealy and Warren Kole as a pair of bickering detectives ordered to attend couples therapy.
Zehetner will play a rookie female detective who assumes control of the digital technology unit, according to Deadline.
Though Travis (Ealy) shows romantic interest in the new recruit, she is more interested in his partner Wes (Kole).
Zehetner has previously played recurring roles on Mad Men, Grey's Anatomy and Heroes.
She also appeared in a 2010 episode of Southland and starred opposite Joseph Gordon-Levitt in 2005 film Brick.
Former Lost and FlashForward actress Sonya Walger recently signed up to play Travis and Wes's psychiatrist on Common Law.
The show is currently shooting in New Orleans and will premiere in 2012 on USA.
> Jack McGee lands Common Law role
> Amy Acker joins Common Law pilot