Theo Epstein's next chapter in baseball is already starting. Epstein, the former Red Sox and Cubs executive who built World Series champions in both Boston and Chicago, will join Major League Baseball as a consultant regarding on-field matters, Commissioner Rob Manfred announced Thursday.

In his new role with the league, Epstein will focus on determining how various rule changes might affect the game. He'll work with baseball analytics experts from the Commissioner's Office and the 30 MLB clubs.

• Epstein a superstar in his field

"Theo is one of the most accomplished and thoughtful people in our sport," Manfred said in a statement. "I am grateful that he has accepted our invitation to complement our ongoing efforts and provide his insights on making the best game in the world even better for the next generation of fans."

Epstein stepped down as the Cubs' president of baseball operations in November, his ninth season with the team, with one year remaining on his contract. At the time, he said he hoped to have a third chapter in baseball, and that he would stay engaged with the game and help "as best I can." That chapter is starting even sooner than he thought.

"It is an honor to assist the efforts by Major League Baseball and the Competition Committee to improve the on-field product, and I appreciate Commissioner Manfred asking me to be a part of these important conversations," Epstein said in a statement Thursday. "As the game evolves, we all have an interest in ensuring the changes we see on the field make the game as entertaining and action-packed as possible for the fans, while preserving all that makes baseball so special. I look forward to working with interested parties throughout the industry to help us collectively navigate toward the very best version of our game."

Epstein mentioned when he left the Cubs that he’s had ongoing conversations through the years with Manfred and other top executives in the league office. Now, those have turned into an official role with MLB.

The area on which Epstein will be consulting is of special interest to him. When he left the Cubs, Epstein expressed his belief that executives like him, and the analytical strategies they pioneered, have had unintended consequences for the game.

"The executives like me who have spent a lot of time using analytics and other measures to try to optimize individual and team performance have unwittingly had a negative impact on the aesthetic value of the game and the entertainment value of the game in some respects," Epstein said at the time. "We need to find a way to get more action in the game, get the ball in play more often, allow players to show their athleticism some more and give the fans more of what they want."

But those strategies also made Epstein one of the most successful executives in modern baseball, and earned him his reputation as one of the smartest. Epstein was the architect of two curse-shattering World Series champions -- the Red Sox team that ended the Curse of the Bambino in 2004, and the Cubs team that won the franchise's first World Series title in 108 years in 2016.

In Epstein's 29 years in Major League Baseball -- including his nine seasons as Cubs president of baseball operations from 2012-20 and nine as Red Sox general manager from 2003-11 -- he won three World Series, in 2004 and '07 with Boston and '16 with Chicago. That makes him one of only five executives to lead multiple organizations to a World Series championship.