Farrell had previously revealed his involvement in the small-screen drama, but the cable network did not officially confirm the casting for the eight-episode, second season until Tuesday.
Production on the sophomore season of the show is to begin later this fall in California, with Justin Lin directing the first two episodes. The program was created and written by Nic Pizzolatto.
"Three police officers and a career criminal must navigate a web of conspiracy in the after-math of a murder," a Season 2 synopsis teased.
Additional casting will be announced as it is confirmed, HBO said.