The Showtime pilot stars Kathryn Hahn and Steve Coogan, who stepped in when original star Philip Seymour Hoffman died shortly after shooting the pilot, according to The Hollywood Reporter.
'Happyish' will chronicle the pursuit of happiness for an advertising executive (Coogan).
Whitford will play Jonathan Cooke, an advertising industry legend and the boss of Coogan's character Thom Payne.
The role of Cooke was originally filled by Rhys Ifans, who has since departed the pilot. 'Happyish' creator Shalom Auslander, who penned the script, will also serve as the director.