The Brewers made the announcement, saying the contract included a vesting option for the 2018 season. Earlier in the afternoon, team owner Mark Attanasio was on stage during a question-and-answer session at a fan event and said a deal was in place.
"Matt is an established top-of-the-rotation pitcher who provides our staff with experience and quality depth," general manager Doug Melvin said.
A person familiar with the negotiations, who was not authorized to speak publicly about the contract, told The Associated Press the four-year deal was worth $50 million with an extra $1 million per year in reachable performance bonuses for a starter.
The 30-year-old righty went 10-6 with a 3.82 ERA last season for the Chicago Cubs and Texas Rangers. He missed most of the first two months while recovering from an injury that affected his side and back.
Garza will join Yovani Gallardo and Kyle Lohse as Milwaukee's top starters. He is 67-67 with a 3.84 ERA in eight seasons with Minnesota, Tampa Bay, the Cubs and Texas.
Garza was looking forward to pitching - and hitting - back in the NL Central.
"It's fun. I like the Central, I like pitching in the Central," Garza said in a conference call. "I like swinging the bat in the big parks."
The move also adds depth to the staff and puts less pressure on young pitcher such as Wily Peralta and Tyler Thornburg in the back end of the rotation.
"We've said now for a couple of years that we're focusing on pitching and pitching depth," Attanasio told reporters. "You can never have enough pitching depth, and I would argue we have as much pitching depth as we've had (in) my 10 seasons of ownership."
Garza was the MVP of the 2008 AL championship series, beating Boston twice while with Tampa Bay. He also has thrown the only no-hitter in Rays' history, on July 26, 2010, against Detroit.
His signing had been rumored for days, though the Brewers were seemingly a surprise suitor for Garza's services. The team issued a statement Thursday that they were in talks with Garza but hadn't reached a deal then.
"These deals can go to the 11th hour and then not come together," Attanasio said. "So you don't know until you know."
(Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)