The Brewers signed Suppan to a $42 million, four-year deal before the 2007 season, but he never pitched as strongly as he did in his three previous seasons in St. Louis.
With the Cardinals, he won a World Series and was picked the NLCS MVP in 2006.
"I was committed to winning and to this day I still am. Nobody is more disappointed than I am with how things have turned out," Suppan said in a statement. "I enjoyed my time here in Milwaukee as both a player and a member of the community."
His numbers steadily declined in Milwaukee, going 29-36 with a 5.08 ERA in 97 starts and 13 relief appearances. Suppan made two starts this year before being sent to the bullpen -- he was 0-2 with a 7.84 ERA.
"We didn't see Jeff returning to the rotation," general manager Doug Melvin said.
The Brewers owe the 35-year-old Suppan the remainder of his $12.5 million salary this season as well as a $2 million buyout of his 2011 club option. Suppan had been a favorite of owner Mark Attanasio, but Melvin said Attanasio wasn't consulted on the timing of the move.
"The money didn't have anything to do with it in that regard," Melvin said. "Mark is very fond of Jeff and I think we all wanted to extend this as long as we could because of our respect for Jeff."
While Suppan was well liked by the organization, he became the prime target of fans' frustrations because of his ineffectiveness and big salary combined with the club's failure to meet expectations since its postseason run in 2008.
In recent weeks, he's been booed simply entering the game from the bullpen and a comment on one message board immediately after the news said "Yes!!!" 48 consecutive times.
"It couldn't have been fun for Jeff to go out there and read the articles," Melvin said. "That's not fun, nobody likes to read that stuff."
Suppan's single-season salary is the highest ever in team history, and his $42 million contract was the biggest in total dollars when he signed it. All-Star left fielder Ryan Braun's $45 million, eight-year deal surpassed that in 2008.
Melvin said that Suppan's contract after the 2006 season was in line with the big pitching deals of Barry Zito ($126 million, seven years), Gil Meche ($55 million, five years) and Ted Lilly ($40 million, four years).
"When you enter into free-agent contracts, guys, it's one of the riskiest things to do," Melvin said. "We all get excited about the free-agent people that are out there, but there are not a lot of free-agent contracts with pitchers that you do get the full length of performance."
Suppan acknowledged that his new role as a mop-up reliever was difficult.
"It's frustrating," Suppan said at the end of the last homestand after allowing four runs in a tie game against the Mets May 30 that saddled him with his final loss as a Brewer.
"I'm working hard and trying to be effective in this new role and trying to be ready when they need me to pitch. It's a learning process. I'm trying the best I can."
Suppan allowed 13 runs in his final five outings with the Brewers and his numbers as a starter steadily declined, going from 12-12 with a 4.62 ERA in 2007 to 7-12 with a 5.29 ERA last year.
Suppan also failed in his lone big-game situation with the Brewers after his strong 2006 postseason run with the Cardinals.
Suppan started Game 4 of the NL divisional series against Philadelphia in 2008, but allowed a leadoff homer to Jimmy Rollins and left the game trailing 5-0 after the third inning. Milwaukee went on to lose 6-2, ending its first postseason appearance in 26 years.
The Brewers have gone 103-116 since, including a 23-34 mark so far this season.
"We think we can turn this thing around. We've pitched better here recently, but we've got to do it for a longer period of time," Melvin said. "We keep the game close enough to give our offense a chance to win ballgames."
To fill Suppan's roster spot, the team will bring up reliever Chris Smith, who is 2-1 with a 1.71 ERA and 16 saves at Triple-A Nashville.