McKellen will voice the monstrous Snowmen in Steven Moffat's festive episode which will be broadcast on BBC One on Christmas Day.
The actor is known for his roles in blockbusters including Lord of the Rings, The Hobbit, X-Men and The Da Vinci Code.
The news was revealed by Radio Times reviewer Patrick Mulkern who admitted that he initially thought that the Snowmen were voiced by Sir Partick Stewart.
In his preview of The Snowmen, Mulkern also praises Jenna-Louise Coleman for her portrayal of Clara. The reviewer says: "We have a proper introduction to Matt Smith’s new co-star Jenna-Louise Coleman, who is dazzling and perky as Clara, and not as cocky as her looky-likey Oswin in Asylum of the Daleks."
Read the full preview on the Radio Times website.