Fowler, 27, hit .263 with 18 doubles, 12 home runs, 42 RBIs, 19 stolen bases, 65 walks and a .369 on-base percentage in 119 games with Colorado last season, starting 106 games in center. In 2012, he hit .300 in 143 games with a .389 on-base percentage.
"We're happy about it," Astros general manager Jeff Luhnow said. "We've been working on it for more than a few days now, and I think it really fits with our offseason strategy. We want to focus on pitching, but we want to be able to bring in an offensive catalyst, and I think this type of player for us is ideal. ... It's a pretty exciting overall package for us."
Fowler will be in the second year of a two-year contract that will pay him $7.35 million in 2014, and he has one remaining year of arbitration left in '15 before he can become a free agent. He'll easily become the Astros' highest-paid player, backing up the club's commitment to spend some money this winter.
"I'm very excited about the opportunity," Fowler said. "The Rockies drafted me, so I'm definitely thankful they took that chance so I could get my career started. Getting traded, you can always look at it like it's a new beginning, and I'm excited about the team Houston has and the young guys, and I'm excited to get started."
The Astros' wealth of young starting pitchers -- they used a six-man rotation late last season to accommodate them -- helped make it easier to move Lyles, a supplemental pick in the 2008 First-Year Player Draft who's struggled to find consistency. He went 7-9 with one save and a 5.59 ERA in 27 games (25 starts) with Houston last season and was looking forward to returning to the National League.
"I'm thankful and appreciative of the Astros and everything they've done for me, drafting me and bringing me up," Lyles said. "I couldn't say more about Houston and their organization. But I'm turning a new leaf and headed to Colorado, and hopefully I can turn things around and get more consistent and have some good years in Colorado."
The Astros lose a fan favorite in the high-flying Barnes, who hit .240 with eight homers and 41 RBIs in 136 games in his rookie season in 2013, while playing a tremendous defensive center field. But with L.J. Hoes and Robbie Grossman returning, and top prospect George Springer on the rise, Barnes was expendable.
"I'm blessed to have the opportunity Jeff Luhnow gave me and [owner] Jim Crane and all they've done for me in getting that opportunity to play in the big leagues," Barnes said. "I'm very blessed to have that, and now I'm looking forward to going out to Colorado and playing with them."
Fowler was limited by a sore wrist and knee last season, but he told reporters Tuesday he was healthy. He walked 65 times and struck out only 105 times in 492 plate appearances in '13, and he is joining an Astros team that set the Major League record for strikeouts.
In his six-year Major League career with Colorado, Fowler has hit .270 with 120 doubles, 53 triples, 40 home runs, 210 RBIs and 376 runs in 667 games. Fowler was originally selected by Colorado in the 14th round of the 2004 First-Year Player Draft out of Milton High School in Georgia.
Fowler joins an Astros team that is rebuilding and coming off a club-record 111 losses, but he's looking forward to being part of the future.
"There's definitely challenges, but at the same time, you look at the positives, and the positive is we have some young talent here," Fowler said. "They're eager to win and they're eager to put their imprint into the game. That's awesome. Anything I can do to help, I'm going to go out and play hard every day and will see the tide turn."
Luhnow said the arrival of Fowler won't affect Springer, who put up huge numbers last season while playing center field in Double-A Corpus Christi and Triple-A Oklahoma City. Springer is expected to make his Major League debut at some point next year.
"George has the skills to play all three outfield positions, and Dexter can probably play all outfield positions as well," Luhnow said. "It's one of those things we'll cross that bridge when we get to it. But I'd rather have a surplus of athletic, good defensive, good offensive players, than bring players in to profile for a particular position and maybe are lacking some of those other skills."
The Astros' winter figures to be just heating up. The team would still like to add a veteran starting pitcher to go with youngsters like Jarred Cosart, Dallas Keuchel, Brett Oberholtzer and Brad Peacock, as well as bullpen help after leading the league in blown saves last season with 29.
"Despite the lack of transactions, we've been extremely active in pursuing both relievers and starters," Luhnow said. "We just haven't found our match yet. We're going to continue to work hard on it, and I'm confident we'll have another deal or two done by this time next week."