Murphy collapsed and died four days after filming his first scenes for the program's fifth season. The actor had been cast as Ser Denys Mallister, commander of the Shadow Tower and the oldest member of the Night's Watch, and was due to film more scenes.
"We will not be recasting J.J. Murphy," producers D.B. Weiss and David Benioff said in a statement. "He was a lovely man, and the best Denys Mallister we could have hoped for. And now his watch is ended."
Murphy hailed from Northern Ireland, and began his career on stage. He performed for years at the Lyric Theatre in Belfast, and also appeared in films Angela's Ashes and Faraway. He recently finished his scenes as the Village Elder in Dracula Untold, which is scheduled for release October 17.
Game of Thrones season five premieres on HBO in 2015.