Ian McElhinney and Steve Toussaint will appear in the two-part Doctor Who finale.
The Doctor, played by Jodie Whittaker, comes face-to-face with the Cybermen in the last instalment of the current series.
McElhinney, 71, best known for his roles in Rogue One: A Star Wars Story and Game Of Thrones, said: “I very much enjoyed my time on Doctor Who… All in all it was a blast.”
Prince Of Persia: The Sands Of Time actor Toussaint, 54, said: “It was an honour to play a part in the giant of British (and world) TV that is Doctor Who.
“What’s not to like? I had such a great time working with Jodie and ‘the Fam’ – another one off the bucket list.”
The show’s executive producer Matt Strevens said the two-part finale, called Ascension Of The Cybermen and The Timeless Children, will bring series 12 to a “dramatic conclusion”.
Doctor Who continues on BBC One on Sunday at 7.10pm.