This new series will be the first time Jed Mercurio's crime procedural has jumped to BBC One having aired on BBC Two since 2012; it'll air on Sunday 26 March
Each series places a new suspected individual at the forefront of anti-corruption squad AC-12's investigation with the first two focusing on Lennie James' DCI Tony Gates and Keeley Hawes' DI Lindsay Denton. Last year's dramatic run saw Daniel Mays lead the charge as Sgt. Danny Waldron.
This time around it's Thandie Newton - most recently seen stealing scenes in HBO series Westworld - whose DCI Roz Huntley gets investigated after finding herself in the middle of a career-defining case.
Returning to the series are Martin Compston as DS Steve Arnott, Vicky McClure as DC Kate Fleming and Adrian Dunbar as Superintendant Ted Hastings.
Joining the cast alongside Newton are Jason Watkins, Lee Ingleby and Royce Pierrson.
Upon its premiere, Line of Duty became BBC Two's most-watched original drama in ten years. The channel handed it a further two series following a critically successful second run - and a fifth has already been commissioned.
Viewing figures for the third series saw 5.6 million viewers tune in for the finale - a series high.
Line of Duty returns to BBC One on Sunday 26 March at 9pm.