The second series of the British police procedural television programme Line of Duty, was broadcast on BBC Two between 12 February and 19 March 2014.

The series follows the actions of the fictional Anti-Corruption Unit 12. AC-12 is led by Superintendent Ted Hastings (Adrian Dunbar) who is assisted by his team DS Steve Arnott (Martin Compston), DC Kate Fleming (Vicky McClure), and DI Matthew "Dot" Cottan (Craig Parkinson). The unit investigates DI Lindsay Denton (Keely Hawes), the sole survivor of an attack on police officers, and the possibility of a corrupt police officer conspiring to murder a protected witness in the ambush. Jessica Raine stars in a single episode as DC Georgia Trotman. Beginning with this series, Dunbar and Parkinson are credited as main cast members in the opening credits. Supporting characters include DCC Mike Dryden (Mark Bonnar), Jo Dwyer (Liz White), DCS Lester Hargreaves (Tony Pitts), DC Nigel Morton (Neil Morrissey), and Tommy Hunter (Brian McCardie).

The series was created and written by Jed Mercurio, who also serves as an executive producer. Filming took place in Belfast in 2013. Six episodes were directed by Douglas Mackinnon and Daniel Nettheim with cinematographer Ruairi O'Brien. The series received positive reviews and multiple accolades, most notably for Hawes performance as Denton, leading to the commission of a third and fourth series.

On 25 July 2012, the day after the first series had concluded, BBC Two commissioned a second series of Line of Duty from World Productions.^[4][5] Creator Jed Mercurio wrote the series episodes and executive produced it alongside Simon Heath for World Productions and Stephen Wright for BBC Northern Ireland.^[6] Peter Norris produced the series.^[7]

Actors Martin Compston and Vicky McClure returned from the first series.^[8] Adrian Dunbar also returned to the series and was promoted to the main cast.^[9] Craig Parkinson reprised his role beginning in episode three.^[10] Keely Hawes, Robert Lindsay, and Jessica Raine were announced as new members of the cast.^[11] Lindsay departed from the series after two days of filming due to "creative differences" and was later replaced by Mark Bonnar.^[12] Hawes stated that when she first received the script Mercurio had not yet decided if her character would actually be a corrupt police officer.^[13] Supporting cast members include Neil Morrissey,^[14] Brian McCardie,^[15] and Tony Pitts.^[16]

For the second series filming moved to Belfast and began in mid-2013.^[17] The six hour-long episodes were split into two filming blocks with Douglas Mackinnon returning to direct the first block of episodes and Daniel Nettheim directing the second.^[18] Ruairi O'Brien also returned as the series' Director of Photography.^[19] The headquarters of Invest Northern Ireland doubled as Anti-Corruption Unit 12's office building while the exterior of Belfast Central Library served as the police headquarters façade.^[20] One scene filmed with McClure, Compston, and Bonnar covered 18-pages of a script.^[21] Due to the success of the second series a third and fourth series was commissioned in April 2014.^[22]