The series stars Colin Morgan as Merlin, Bradley James as Prince Arthur and Anthony Head as King Uther.
The third series of the ‘re-telling’ of the Arthur legends has attracted an average audience of six million viewers and has featured guest appearances by Miriam Margoyles, Warwick Davies and Pauline Collins.
Announcing the commissioning of the fourth series, BBC Drama commissioner Ben Stephenson said the show “continues to perform outstandingly well against X Factor and offers audiences an alternative treat on Saturday nights.”
Johnny Capps and Julian Murphy, executive producers for Shine TV who makes the series, said they were “delighted with the continuing success of Merlin, and relish the chance to take the series to the next level with the long-awaited arrival of the Knights of the Round Table.”