The three will join two previously announced stars, Irish actor Colin Farrell and U.S. actor Vince Vaughn, in the eight-part miniseries, which was a big hit for HBO earlier this year and received five Primetime Emmy awards.
The second season is in production in California and revolves around three police officers, a career criminal and a murder, HBO said.
Farrell, 38, will play compromised detective Ray Velcoro, and Vaughn, 44, will star as criminal mastermind Frank Semyon in the series from writer Nic Pizzolatto.
HBO said McAdams, the 36-year-old Midnight in Paris actress, would play an uncompromising and ethical sheriff, while Lone Survivor actor Kitsch, 33, will play a California Highway Patrol motorcycle officer.
Reilly, a 37-year-old English actress, will play Semyon’s wife, Jordan, a former D-list actress.
Fast & Furious director Justin Lin will direct the first two episodes. A premiere date for the second season has not been announced.
The first season of True Detective was set in Louisiana and centered on a series of satanic murders, pairing seasoned film stars Matthew McConaughey and Woody Harrelson.
The show’s January premiere helped establish buzz around McConaughey before he won his first best actor Oscar for Dallas Buyers Club.