The 44-year-old Emmy and Tony winner will guest-star in four episodes of the premium channel's upcoming series. She'll play Rebecca, the long lost college roommate of Laura Linney's character, Cathy, who comes back into her life and turns it upside down.
The Big C follows Cathy, a schoolteacher, wife and mother who's diagnosed with a fatal form of cancer and tries to reclaim her life.
Nixon, who battled breast cancer in 2006 and is in remission, can currently be seen alongside her Sex and the City co-stars in the big-screen sequel.
The Big C premieres Monday, Aug. 16 at 10:30/9:30c.
Will you tune in to see Nixon on The Big C?