Now Hollywood insiders are tipping Farrell to be one of four leads in the next season of the show.
President of HBO programming Michael Lombardo said that this season's scripts are even "more exciting" than the first.
"Great writing attracts great actors," he added when asked about casting rumours.
Farrell is in good company now that he is in the mix too joining big names such as Brad Pitt, Christian Bale and Taylor Kitsch as speculation mounts as to who will be recruited to pin on their detective's badges.
The Dubliner has remained tight-lipped about whether he is in talks for the prestigious role.
True Detective is reportedly set in LA next time around.
The City of Angels is a long way from Ballykissangel but it would signal a return to his roots of sorts for the Castleknock native.
The BBC drama signalled Farrell's big break into the world of acting and now it looks like he could be set for a return to the small screen.
He has racked up an impressive list of movie titles including Phone Booth and Seven Psychopaths.
Farrell starred alongside Harrelson in the latter and now it looks like he could be taking over where Harrelson left off on the set of the HBO drama.
True Detective picked up 12 Emmy nominations including a nod for Best Drama and will now battle it out against the monster shows such as Game of Thrones, Breaking Bad and Downton Abbey.
The show is the latest in a string of critically-acclaimed hits from the US pay-per-view channel which transformed small-screen output in the early noughties with the likes of The Sporanos, Sex and the City and The Wire.
HBO president Michael Lombardo indicated recently that all would be revealed in a matter of weeks about the new cast for True Detective.
The unusual decision to entirely replace the cast every season has Hollywood abuzz with anticipationas to who will get the plum gigs.