The 21-year-old defenseman, who was a restricted free agent, had NHL career highs in goals (10) and points (32) in 79 games with the Carolina Hurricanes last season, his third in the League. He also played in his first NHL All-Star Game.
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"I wanted to be there for a long time," Hanifin told the Flames website. "There's a really bright future and I want to be a part of it for the long run."
He was traded to the Flames by the Hurricanes with forward
Elias Lindholm
for defensemen Dougie Hamilton and Adam Fox, and forward Micheal Ferland on June 23.
"It's a big commitment," Hanifin said. "I know it took a bit of time, was a bit of a process, but I was confident. I knew it'd get done. I wanted to be in Calgary really badly. And obviously with the situation there, it's been a busy off-season for (general manager) Brad [Treliving] and the entire staff there.
"I don't know too much about the city but I know a few guys on the team and they said it's a great city and hockey town. It's definitely something I want to be a part of."
Carolina selected Hanifin No. 5 in the 2015 NHL Draft. He has 83 points (18 goals, 65 assists) in 239 NHL games.
"For his game, you can count on one hand how many players that have done what Noah has done, playing that position at that age in the League," Treliving said. "At 18, 19, 20, he's pushing 300 games played. To me, he's just scratching the surface. He's a pup. We think there's considerable upside here.
"The biggest thing in watching Noah last year; the game slowed down for him. He's an elite skater and gets around the ice as well as anybody, especially on the back end, but he took that extra second, that extra pause with the puck, he had that extra confidence to hold onto it a little bit longer and looked people off a little bit more, and you find the game slows down for you. When I look at his game, it's starting to slow down for him. I think he's still got growth on both sides of the puck. Offensively, at that age, he had 10 goals from the back end with not a lot of power-play time. I think you'll see that area continue to grow, as well as the defending side."
Hanifin said he was thrilled to be reunited with Bill Peters, his coach with Carolina in his first three NHL seasons.
"I think my first few seasons I've definitely improved offensively a bit and have more confidence with the puck," Hanifin said. "I can do even more offensively too, be more aggressive and hold pucks longer. Bill, I know he wants us to posses the puck and that's something I want to be a big part of. I think there's parts all over my game I can improve on. I'm still only 21. When I'm 26, 27, I want to be one of the best defensemen in the League. It's going to be an ongoing process. I'm excited about it."
Treliving said the fact Peters has coached Hanifin was a big reason the Flames were willing to make a six-year commitment to a player who has yet to play a game for them.
"It's unique, no question," he said. "Having said that, we probably know him better than anybody could in a situation like that. We've watched the player like that. He's a player we've been focused on for a while, and when you layer the fact that Bill [Peters] is here now and has coached him the past three years, we probably have as much internal intelligence on the player that you can have for not having him played with you."
NHL.com correspondent Aaron Vickers contributed to this report
