The psychological drama, which is written by Allan Cubitt, stars Gillian Anderson as a detective hunting a serial killer (Jamie Dornan).
Its was the channel’s biggest drama series launch in eight years when it debuted last year and is enjoying rave reviews for its second series which is attracting audiences over more than 3m.
Cubitt has now confirmed that fans will be treated to a 90-minute series finale on Thursday 18 December 2014.
He said: “I’m grateful to the BBC for allowing me the opportunity to finish the second series with a feature length episode.
“It’s a real vote of confidence in the show and allows me the chance to explore the issues the drama deals with in real depth.”
Ben Stephenson, Controller BBC Drama Commissioning added: “This series has such a wonderfully shocking conclusion that it’s only fitting viewers should be treated to a feature length finale to relish.”
