He died peacefully in his sleep Monday, the organization said.
"We are heartbroken to share that our beloved husband and father has passed away," said a family statement from Seaver's wife, Nancy, and daughters, Sarah and Anne. "We send our love out to his fans, as we mourn his loss with you."
Seaver played 12 seasons with the Mets, winning the National League Cy Young Award, honoring the league's best pitcher, three times.
After having been a league-wide joke for the franchise's hapless play since their inaugural season in 1962, the team, which was dubbed the Miracle Mets, was able to overcome years of failure and win the 1969 World Series as Seaver won his first Cy Young Award.
A statement from Mets CEO Fred Wilpon and his son, Chief Operating Officer Jeff Wilpon noted Seaver’s nicknames—”the Franchise” and “Tom Terrific.” Seaver’s number, 41, was the first number the organization ever retired, in 1988, the duo said.
“We are devastated to learn of the passing of Mets legend and baseball Hall of Famer Tom Seaver,” the pair said. “ … We will always remember Tom for his passion and devotion to his family, the game of baseball, and his vineyard.”
He's credited with 311 wins, 3,640 strikeouts and a 2.86 earned-run average during a career that started in 1967 and ended in 1986.
"Tom Seaver's life exemplified greatness in the game, as well as integrity, character, and sportsmanship — the ideals of a Hall of Fame career," Hall of Fame Chairman Jane Forbes Clark said. "As a longtime member of the Hall of Fame Board of Directors, Tom brought dignity and wisdom to this institution that will be deeply missed."
Seaver also played parts of six seasons with the Cincinnati Reds, parts of three with the Chicago White Sox and one with the Boston Red Sox.
National League Baseball Commissioner Robert Manfred said, “I am deeply saddened by the death of Tom Seaver, one of the greatest pitchers of all-time. Tom was a gentleman who represented the best of our National Pastime.”