The show is to begin filming this fall for a 2014 premiere on the cable television network.
Hartnett will play Ethan Chandler, "a charming American," while Green will play Vanessa Ives, "a seductive and formidable beauty full of secrets and danger," a synopsis said.
The show was created, written and executive produced by John Logan, whose screenwriting credits include "Hugo," "The Aviator" and "Gladiator" -- each of which was nominated for an Academy Award.
"Penny Dreadful" is being executive produced by Logan's Desert Wolf Productions, along with Oscar-winning "American Beauty" director Sam Mendes.
Juan Antonio Bayona, who helmed "The Orphanage" and "The Impossible," is to direct the first two installments of the 8-episode series.