Mark Gatiss also appeared on PBS skein "Sherlock"
Gatiss joins Pedro Pascal as the newest member of the ever-growing cast. The network would not reveal who Gatiss would play in the HBO drama.
The British thesp has had several jobs on the BBC show “Doctor Who” including writer and actor. He also plays Sherlock Holmes’ brother Mycroft on the PBS show “Sherlock.”
“Game of Thrones” is currently filming the fourth season, which will air sometime next spring.