Sandy Alderson, who left his post as the Mets’ general manager last summer because of a cancer recurrence, will return to his baseball roots now that his health has improved.

The Oakland Athletics announced on Tuesday that Alderson, 71, would rejoin the club as a senior adviser in the baseball operations department, two decades after he left the team in the hands of Billy Beane.

Alderson announced on Saturday at the New York Baseball Writers’ Awards dinner, where he received an award honoring his career, that he had been cancer-free for four months. He received a standing ovation.

Alderson began his baseball career with the A’s in 1981 and was one of the sport’s pioneers in sabermetrics. Back then, he counseled Beane, his successor, whose reliance on advanced statistics kept the small-market team competitive and was famously documented in the book “Moneyball.”

“His mentorship and friendship have been invaluable to me over the course of my career, and I look forward to the expertise and perspective he will add at every level of the organization,” Beane, the A’s executive vice president of baseball operations, said of Alderson in a statement issued by the team.

Referring to David Forst, the current A’s general manager, Beane added, “David and I couldn’t be more excited to bring him back to Oakland.”

Alderson was the architect of the A’s teams that won three straight American League pennants from 1988 to ’90, as well as the 1989 World Series. He left in 1998.

“I am really excited to return to the A’s and the Bay Area,” Alderson said in the team’s statement. “I look forward to being as helpful as I can to Billy, David and the rest of the baseball operations staff.”

After his 17-season stint with the Athletics, Alderson spent seven years working in Major League Baseball headquarters and four years as the chief executive of the San Diego Padres, before going back to the M.L.B. commissioner’s office for a year.