Cameron, a 2001 All-Star, hit .243 with 25 home runs and 70 RBIs in 120 games in 2008.
"I didn't think my option would get picked up," Cameron told the Milwaukee Journal Sentinel. "This was a surprise, to be honest with you."
The Brewers could have paid a $750,000 buyout to the three-time Gold Glove winner, who made 119 starts in center field and committed only one error.
The 35-year-old was suspended by the league for 25 games to open the season for using a banned stimulant last year, costing him about $790,000 in salary.
"In a statistical analysis, he ranked as the sixth-best center fielder in the major leagues," Brewers general manager Doug Melvin said, according to the Journal Sentinel. "And he improved our pitching by playing center field the way he did.
"The only difficult thing is that we're so right-handed," Melvin added, regarding the lineup. "But we felt he has value. When you look at his contract, we paid him $7.5 million average for two years. That's the way we viewed it."
Monday was the last day the Brewers could exercise Cameron's contract option.
"I'm just thankful to get another opportunity to be involved with a team that's on the verge of knocking some doors down on a yearly basis," Cameron said, according to the newspaper.
Information from The Associated Press was used in this report.