The film, in which the Pearl Harbour star plays an Internet entrepreneur desperately trying to keep his business and personal afloat, opens in New York on the same day.
Hartnett will be joined by castmates and producers as he brings Big Apple business to a close.
The cast of August includes Naomie Harris, David Bowie, Rip Torn, Emmanuelle Chriqui and Robin Tunney.
Source: WENN