The left wing, who turned 19 on Sunday, was the No. 1 pick in the 2020 NHL Draft.
"It was a really easy process," Rangers general manager Jeff Gorton said. "We worked with his agency and got things done really quick here."
Gorton said he hopes Lafreniere will arrive to New York in early November to prepare for training camp. He will not return to his junior team, Rimouski of the Quebec Major Junior Hockey League.
The 2020-21 NHL regular season is targeted to begin Jan. 1, 2021.
"Obviously, we're really excited about getting him signed and becoming a Ranger and everything that goes along with it," Gorton said. "Looking forward to the first time we can actually see him on the ice."
Lafreniere was named MVP of the QMJHL and the Canadian Hockey League Player of the Year for the second consecutive season after he scored 112 points (35 goals, 77 assists) in 52 games last season. He's the first back-to-back winner of each award since Sidney Crosby (2003-05) and was also named the MVP and best forward at the 2020 IIHF World Junior Championship, where he helped Canada to a first-place finish.
"It was an unreal feeling," Lafreniere said Oct. 6 during the 2020 draft. "Obviously, the New York Rangers are a great organization and for me, I'm really honored to join them. When I heard my name, we've been waiting for a long time, so it was something really special for me and for my family."
Lafreniere could play in the 2021 WJC if the NHL season doesn't start Jan. 1. The tournament will be held Dec. 26-Jan. 5 at Rogers Place in Edmonton without fans in attendance, a secure-zone bubble similar to what the NHL used for the Stanley Cup Playoffs.
"We're talking about those scenarios and what's going to happen," Gorton said. "Right now, our focus is get him here as soon as we can and have him start training and be here and start focusing on the NHL season. We'll take it as it comes as far as the World Juniors or any other situation that might come up."
Lafreniere was the second player chosen No. 1 by the Rangers (Andre Veilleux in 1965) and first since the universal draft was adopted in 1969, when all junior players of qualifying age were eligible for selection.
NHL.com senior writer Dan Rosen contributed to this report
