The series will star Toni Collette.
Written by Oscar winner Diablo Cody, "United States of Tara" looks at a woman (Collette) with multiple personality disorder.
According to The Hollywood Reporter, Corbett will play the main character's husband, a contractor trying to deal with his wife's condition.
Craig Gillespie will direct the "Tara" pilot, which will shoot next month in Los Angeles.
This will be Corbett's second Showtime pilot in recent years, following a co-starring role in the premium cable network's 2006 comedy "Manchild."
While many viewers will always think of Corbett as Aidan on HBO's "Sex and the City" or as the main character on FX's "Lucky," for many more he'll always be Chris from "Northern Exposure." Corbett's feature credits include "Raise Your Voice" and "Raising Helen."