The show stars Jurassic Park actress Laura Dern as Amy, a self-destructive woman who has a spiritual awakening and decides to live an enlightened life, complicating her relationships with family and friends.
Deadline reports that Sharp will now play the Dern character's new boss. Mos Def is believed to have left the role after failing to reach a deal with HBO.
Death at a Funeral star Luke Wilson will appear alongside Dern and Sharp as Levi, Amy's drug-addicted ex-husband.
The new show is being produced by School of Rock scribe Mike White, who also directed the pilot. Filming on the series began on Monday in Los Angeles.