Valverde, 28, was 1-4 with a 2.66 ERA and a Major League-leading 47 saves for the Diamondbacks in 2007. His 47 saves also marked a career-high total, and he appeared on the National League All-Star team for the first time.
The Arizona franchise-record 47 saves also ranked tied for 15th all-time in a single season, and Valverde also struck out 78 hitters in 64 1/3 innings while walking 26 and allowing 46 hits.
"In Jose Valverde, we're adding an All-Star closer and one of the best stoppers in the game. He led the Majors in saves last year and most of them came in tight, one-run situations for a team that was in the thick of a pennant race," general manager Ed Wade said. "He's a huge addition to our pitching staff.
"We believe that Chad Qualls would have done a fine job for us on the back end, but acquiring a pitcher like Valverde, who has excelled in the ninth inning, made tremendous sense for us."
After making sweeping changes to the bullpen, Wade likes how the back end is shaping up. Manager Cecil Cooper will ultimately decide who pitches when, but Wade believes the club has extremely capable candidates to absorb those crucial seventh and eighth innings.
"Doug Brocail turned in great numbers last year," Wade said. "And Oscar Villarreal is a durable guy who can give multiple innings. Cooper can use him in a lot of latter stages."
Wade also mentioned Geoff Geary, Mark McLemore, Wesley Wright and Ryan Houston as contributors. Felipe Paulino and Chris Sampson will contend for rotation spots but could also receive bullpen assignments.
"I like the way we're set up," Wade said. "We gave up a lot of talent in Qualls, Chris Burke and Juan Gutierrez, but adding Jose Valverde puts us another step closer to being a championship team."
Burke wasn't entirely shocked by the news that he was traded, considering his fate was pretty much decided when the club signed second baseman Kazuo Matsui. Still, Friday's announcement put to an end a tense couple of weeks during which Burke wondered about his future.
"There's some relief finally having a destination," Burke said. "I was prepared to be traded ever since we signed Matsui. There's some relief in that, but at the same time, it's surreal that it's finalized and I'm no longer an Astro. It's certainly an awkward feeling."
Qualls' name had surfaced here and there in trade rumors, but the right-hander was still taken back by Friday's news.
"It was hard to take," he said. "I've been with Houston since I got drafted in 2000, and it's all I know."
Qualls spoke with former teammate Russ Springer, who put his mind at ease regarding the Diamondbacks.
"He played for them and he said he liked it there," Qualls said. "They're a contending team. They just added Dan Haren and he's good. Baseball-wise, I think it's going to be great. Family-wise, there are a few things we have to figure out."
Qualls recently was married, and his wife, Tara, is a Houston native. The two were planning to split time between Houston, where her family is, and southern California, where Qualls is from.
Qualls understands trades are part of the business, and although he knew he could possibly be dealt this winter, he felt strongly that he would be back with the Astros in 2008.
"I knew people were asking about me," he said. "It's been like that for the last couple of years. I thought I was going to hang around. Nothing was brewing. All of a sudden, I get a call and bam, it's happening. It's hard to take in and it probably won't soak in for a couple days.
"I'll enjoy the opportunity in Arizona. Your first trade is always tough. This is the only organization I know. That's the way the game goes and I know it's how it goes. But it's hard to swallow."
Wade surmised that he is likely done making moves on the trade front, but he's still working on a couple of free agent starting pitchers. He was hoping to sign Glendon Rusch, who instead went to the Padres.
"There are a couple other people we're talking to and I think there will be an opportunity to add volume to mix and quality, as well."
Alyson Footer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.