The singer and his wife are huge fans of the show and he offered up his services when he heard producers were planning a huge battle scene between the cast regulars and the Army of the Dead.
Stapleton's wife Morgane Hayes confirmed his role by posting a shot of his milky-eyed character lying dead on social media on Monday, and adding the caption: "Episode 3... My wildling is a white walker #got."
Stapleton tells Rolling Stone Country he flew to Ireland to film the bloody scene.
"They knew we weren't actors," he says, "so the direction was basically, 'We're going to place you, and when we tell you to, open your eyes. And they trained us on how White Walkers are supposed to stand up and move when they're first waking up. We had a crash course in that."
The singer, who joins the likes of Ed Sheeran, the members of heavy rockers Mastodon and Coldplay's Will Champion among the musicians granted screen time on the show, admits he had no idea what was going to happen and had to watch the Battle of Winterfell episode with all the other fans.
"Once again, they do a bang-up job of keeping you guessing as to what will happen," he says. "That's why it's the greatest television show certainly of modern times and possibly ever."