The Golden Knights received minor league forward Mikael Hakkarainen in return.
Fleury, however, is contemplating his future after his agent, Allan Walsh, said the three-time Stanley Cup-winning goaltender was caught off guard by the trade, with sources telling ESPN that he found out about it via social media.
"While Marc-Andre Fleury still hasn't heard from anybody with the Vegas Golden Knights, he has apparently been traded to Chicago," Allan said on Twitter before the trade was made official. "Marc-Andre will be taking time to discuss his situation with his family and seriously evaluate his hockey future at this time."
Sources had said there was chatter that Fleury, 36, might retire if he was traded from Vegas.
According to sources, Blackhawks president and general manager Stan Bowman and Fleury had a phone conversation Tuesday afternoon. Bowman and the Blackhawks want to respect Fleury and give him the space and time he needs to make a decision, sources said.
In a statement Tuesday night, Fleury thanked "all the amazing fans in Vegas and my teammates for four incredible years together."
"You embraced me and my family from day one and made playing games at the Fortress one of the great joys of my life," he continued. "We will miss playing in Vegas very much but I am grateful for my time in your city."
Vegas general manager Kelly McCrimmon was defensive about the team's process, saying conversations about a potential trade began at Fleury's exit meeting on June 29.
McCrimmon said he told Fleury that he wasn't sure what the team was going to do next season, but he wanted the goaltender to be fully aware of any discussions. McCrimmon said he last spoke with Fleury's representatives on Saturday.
"We can't contact a player and tell that player that he's been traded if we haven't completed the trade call," McCrimmon said. "It's just a process that you have to go through with the timing of that. Unfortunately, it all leaks out. It just always seems to. It's not a lack of regard for the players. And again in this situation, Marc-Andre was fully abreast of discussions all the way through, not just in relation with the team he ended up being traded to, the Chicago Blackhawks, but any other conversations that I had previously."
This organization, this city and this fanbase will forever be grateful to Marc-Andre Fleury for the impact he's made on and off the ice in just four years. We wish Marc-Andre and his family the best in this new chapter of their lives. #VegasBorn 🌸 pic.twitter.com/tiXn3d3wm0— Vegas Golden Knights (@GoldenKnights) July 27, 2021
Fleury, a 17-year NHL veteran, won his first Vezina Trophy in 2021 with Vegas. He went 26-10-0 with a career-best .928 save percentage and 1.98 GAA as the Golden Knights had the league's second-best record in the regular season, trailing only the Colorado Avalanche.
"The opportunity to acquire a Vezina-winning goaltender is rare and one you cannot pass up," Bowman said in a statement. "Marc-Andre improves our goaltending, strengthens our team defense and will have a huge impact on the overall development of the Blackhawks.
"Having a goaltender like this on our team will put the talent we currently have on our roster in a better position to achieve sustained success. The entire organization is thrilled to have this future Hall of Famer on our team and his reputation of being an excellent teammate on and off the ice precedes him."
Fleury and Robin Lehner won the William Jennings Trophy as the goalie tandem with the best save percentage this past season. In the playoffs, Fleury led the Golden Knights to series wins against the Minnesota Wild and the Avalanche before falling to the Montreal Canadiens in the semifinals.
It's the first time in 20 years the reigning Vezina winner was traded before the next season. Buffalo traded Dominik Hasek to Detroit on the first day of free agency in 2001.
Fleury, who won all three of his Cup titles with the Pittsburgh Penguins, had been the Golden Knights' starting goaltender from the team's inception and led Vegas to the Stanley Cup Final in its first season.
It had been an awkward time-share after the Golden Knights brought in Lehner at the 2020 trade deadline -- in a deal, coincidentally, with Chicago. Fleury and Lehner got along well off the ice, even as coach Peter DeBoer switched between the goalies over the past season and a half.
During the 2020 playoffs, in which Lehner became the primary starter, Fleury's agent tweeted an edited picture of Fleury being stabbed by a sword that had DeBoer's name in it.
McCrimmon said he didn't think there would be the same "appetite" next season for Fleury and Lehner to split the net 50-50, which is what precipitated the trade. Both goaltenders combined for $12 million against the cap, with Fleury entering the final year of a contract that pays him $7 million annually.
"My job is to make our team better, and you need cap space to do that," said McCrimmon, who wouldn't say if the team had also considered trading Lehner.
"Marc-Andre wanted to play in Vegas, that never changed," McCrimmon said. "I don't think that's a surprise to anyone on the call; that was his number one preference. With respect to any decisions he might make moving forward, this is a player that is at the very top of his game. I believe he'll be a candidate to play for the Canadian Olympic team, so I sure think he'll play this year, but those are things I'd leave [to him] or others to speak about.
"He was the most popular player I've ever seen in sports. He was the face of the franchise, when you think back to how it all began -- the storybook season, the passion he has for the game both as a teammate and a player that's connected to the fan base. I want to recognize him for his great accomplishments, thank him for his time here. He's had a tremendous impact on our organization, a tremendous impact on our city. For a lot of people, this is a day that is definitely filled with sadness. Certainly I feel all of those same emotions that you do. But I feel I am responsible to put the best team possible on the ice."
Fleury immediately would become the No. 1 goalie for the Blackhawks. Chicago parted ways with longtime netminder Corey Crawford ahead of last season and instead turned to a trio of youngsters: Collin Delia, Kevin Lankinen and Malcolm Subban.
The Blackhawks are in the middle of a rebuild but are accelerating their timeline. On Friday, the team traded for defenseman Seth Jones and agreed on an eight-year contract with an average annual value of $9.5 million.
Chicago has missed the playoffs in three of the past four seasons, finishing sixth last season in the Central Division. The Blackhawks were without captain Jonathan Toews all of last season as he took a personal leave to deal with medical issues. Toews, however, plans to be back for the 2021-22 season.
The Associated Press contributed to this report.