"It came together pretty quickly but the opportunity to secure, in our opinion, a top free agent is an organizational win," Maple Leafs general manager John Chayka said.
"It's an aggressive move, it's not without risk of course, but we just felt given the stage we are at and what he brings to the table, we felt it was worth pursuing."
The 30-year-old defenseman had NHL career highs in goals (22), assists (48), points (70), plus-minus (plus-21), power-play goals (10), power-play points (26), game-winning goals (six), shots on goal (212) and ice time per game (22:42) playing in 73 games this season. He nearly matched his point total from his first four seasons in the League when he had 73 points (13 goals, 60 assists) in 176 games.
Raddysh, who was born in Toronto, had a goal and an assist in seven Stanley Cup Playoff games.
"I couldn't be happier to be joining a great team, a great group of players, and I'm excited to be here for eight years and play for the team I grew up watching," he said.
Raddysh has been on Chayka's radar dating back to the defenseman's time with Erie of the Ontario Hockey League. When Chayka was named general manager of the Arizona Coyotes in 2016, he began closely tracking then-Coyotes top prospect Dylan Strome, who, like Raddysh, played his final season with Erie in 2016-17.
Chayka said he was immediately impressed with the undrafted Raddysh and attempted to sign him with the Coyotes as a free agent before he ultimately signed an AHL contract joining the Chicago Blackhawks organization as an undrafted free agent on May 21, 2018.
"A late bloomer in terms of offensive production (at the NHL level)," Chayka said. "I think for us, we really saw his career as a continual progression and from a points perspective last year it was a large jump. We have a lot of confidence that the fundamentals of his game had consistently improved and there were several jumps that led to this."
The Maple Leafs allowed the second-most goals per game (3.60) in the NHL this season, and see Raddysh having a positive impact in that area.
"The point production is a part of any player's value but the part of the value we were most focused on was his ability to impact the game holistically," Chayka said. "He's a player who plays up against top competition and does quite well, he's a player who breaks the puck out well, he can join the rush and supplement offense, transitions well, defends the blueline well, and when you start adding up all the elements that go into the end result of good production, and the robust play of all of that gives us a lot of confidence that we are getting a defenseman we haven't had in this organization for a long time."
Raddysh has 143 points (35 goals, 108 assists) in 249 regular-season games, all with the Lightning, and four points (two goals, two assists) in 20 playoff games.