The three-time All-Star agreed to a minor league contract with Philadelphia on Wednesday and will report this week to Clearwater, Fla., for extended spring training.
Zambrano is known as much for his volatile outbursts and dugout confrontations with teammates as he is for his 132 wins over 12 seasons and a no-hitter.
With Roy Halladay and John Lannan on the disabled list, the slumping Phillies turned to Zambrano, even though he hasn't pitched in the majors since last September with Miami.
"No promises are made. It's just an opportunity to add some starting pitching," Phillies assistant general manager Scott Proefrock said.
Zambrano, 31, is 132-91 with a 3.66 ERA, including 11 seasons with the Chicago Cubs. He was 16-17 with a 4.66 ERA the last two years.
Zambrano has the right to terminate the deal if he is not added to the major league roster by July 1.
Philadelphia was among the teams with representatives who watched Zambrano throw Monday in Miami. He pitched in winter ball and played for Venezuela in the World Baseball Classic.
"It's low risk, hopefully, high reward," Proefrock said.
When healthy, Zambrano's talent has rarely been an issue.
It's his temper.
He's feuded with teammates, management and umpires in a number of high-profiles blowups.
Chicago placed Zambrano on the disqualified list with no pay and no part in team activities for 30 days in 2011.
Zambrano was placed on the restricted list for six weeks and sent to anger management in 2010 after a verbal altercation with then-teammate Derrek Lee.
In 2009, he was suspended following a tirade against an umpire in which he threw a baseball into the outfield and slammed his glove against the dugout fence.
"He has a competitive temper," Proefrock said. "He's not that way in social settings."
With Halladay and Lannan out, the Phillies have turned to Tyler Cloyd and Jonathan Pettibone to fill the void. Halladay, Cole Hamels and Cliff Lee have a combined seven wins this season.
Proefrock said Zambrano was sincere in wanting to prove he keep his emotions in check—and get batters out.
"We got positive feedback from everyone who has interacted with him recently," Proefrock said. "We're just looking to add some depth and some experience."