The 19-year-old actor will play a character known as Brains on the sci-fi drama, according to his client profile with talent agency United Agents.
Merrick will appear in the 2013 Who episode written by Neil Gaiman, which will reintroduce and revamp classic villains the Cybermen.
Warwick Davis (Life's Too Short), Jason Watkins (Being Human) and Tamzin Outhwaite (EastEnders) will also appear in the episode.
Best known for playing Alo in the fifth and sixth series of E4 teen drama Skins, Merrick has also appeared on BBC One sitcom In with the Flynns and will feature in next year's Richard Curtis movie About Time.
Neil Gaiman has revealed that he wants to make the Cybermen "scary again" with his new episode, which will be directed by Stephen Woolfenden.
Doctor Who returns to BBC One this Christmas with festive special 'The Snowmen', with eight more regular episodes to follow in 2013.
> Doctor Who Christmas special airdate confirmed by BBC
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Photo gallery - Christmas special 'The Snowmen':