The 43-year-old Maddux, long ranked as one of baseball's top pitchers and considered a leading candidate for the Hall of Fame, retired as a player after the 2008 season.
Maddux will assist Cubs GM Jim Hendry.
"I'm looking forward to working my way back into the game and am happy that the Cubs have given me the opportunity to do that," Maddux said. "I started my career with the Cubs and Chicago has always been the best place in the league to play. I'm eager to do whatever I can to help the organization and am looking forward to getting started at spring training."
Maddux had two stints with the Cubs and two with the Los Angeles Dodgers. He also pitched for the Atlanta Braves and San Diego Padres.
"We're thrilled to have Greg back with the Chicago Cubs," Hendry said. "He has such a vast knowledge of all phases of the game and the ultimate respect of everyone from the players to the front office."
Maddux won 355 games in his career. He won the Cy Young Award as the top pitcher in his league four times.
Millions of Getty images now available for free via embed tool
NBC reportedly holds celebs hostage to Jimmy Fallon's show