Coach John Tortorella delivered the surprising news just hours before the league's annual outdoor game, after telling reporters Sunday that Staal would not be available to play.
Staal missed the first 36 games of the season because of lingering effects from a concussion sustained on a hit by his older brother Eric last February.
Tortorella said the decision was made after he and Staal talked at the team dinner Sunday night. Tortorella had consulted with Rangers head athletic trainer Jim Ramsay and specialist Dr. Robert Cantu to confirm he was healthy enough to play and left the decision up to Staal.
"I don't care about anyone else's opinion, are you ready to play?" Tortorella said he asked the 24-year-old. "He said he was, so he's playing."
Tortorella indicated that the nature and the magnitude of the Winter Classic wasn't a factor in the last-minute change.
"I need a yes or a no. I got a yes from my trainer, a yes from my doctor and more importantly I got a yes from the player. He's going to play. I don't care if we're playing in the creek somewhere, he's going to play," Tortorella said.
Staal was cleared for contact last week and has been practicing fully with the team ever since.
When asked Sunday if he expected Staal to be available, Tortorella said he did not and that he would stick with the same lineup from Friday's 4-1 win over Florida.
"Nothing has changed," Tortorella said about Staal's status on Sunday. "Just because we skated outdoors doesn't change anything that's gone on the past couple of weeks."
In terms of managing expectations given Staal's lengthy absence, Tortorella said they will ease him in, depending on how he performs.
"As far as the minutes and the things that go along with Marc Staal, that's going to take time as far as where he's going to sit in our lineup. He'll play on the third pair today and we'll make judgments as we go through," Tortorella said. "We're not changing, we're not putting him in a top-four position and we'll make judgments about his game as it goes along here."
Rangers defenseman Jeff Woywitka was a healthy scratch to make room for Staal.
Staal's brother Jordan, who was hampered by multiple injuries last season, made his season debut in last year's Winter Classic with the Pittsburgh Penguins.
Katie Strang is a hockey writer for ESPNNewYork.com.