She'll play Detective Chief Inspector Joanne Davidson, the senior investigating officer of an unsolved murder, whose unconventional conduct raises suspicions at AC-12.
Best known for her roles in Trainspotting, Gosford Park, State of Play, No Country for Old Men, Boardwalk Empire and, most recently, The Victim and Giri/Haji.
She will start work on Line of Duty series six when filming begins next year, opposite series leads Martin Compston, Vicky McClure and Adrian Dunbar, who are also confirmed to return.
Speaking about the latest signing, Line of Duty writer and showrunner Jed Mercurio said "We're honoured that Kelly Macdonald will join Martin, Vicky and Adrian in Series 6 of Line of Duty. DCI Joanne Davidson will prove the most enigmatic adversary AC-12 have ever faced."
CEO and Creative Director of World Productions Simon Heath added “The Line of Duty team have always been huge fans of her work, so we’re thrilled Kelly has agreed to join us this series to pit her wits against AC-12.”
Piers Wenger, Controller of BBC Drama, says: “We’re delighted that Kelly Macdonald is coming on board for series six. She’s one of the UK’s most versatile actors and we’re excited for viewers to see what Jed’s scripts have in store for her when she joins the Line of Duty team.”
The most recent episode of Line of Duty, series five’s finale on BBC One back in May, is the most watched programme of the year so far, with a 28-day figure of 13.7 million viewers across all TV and online viewing.
Line of Duty returning to BBC One
*Please not photograph is from The Victim and not from Line of Duty.