Miller died at his home in Manhattan at 5:30 a.m., said his daughter Susan Miller. He had been diagnosed with liver cancer in August.
"All players -- past, present and future -- owe a debt of gratitude to Marvin, and his influence transcends baseball," current union head Michael Weiner said. "Marvin, without question, is largely responsible for ushering in the modern era of sports, which has resulted in tremendous benefits to players, owners and fans of all sports."
In his 16 years as executive director of the Major League Players Association, starting in 1966, Miller fought owners on many fronts, winning free agency for players in December 1975. He may best be remembered, however, as the man who made the word "strike" stand for something other than a pitched ball.
"I think he's the most important baseball figure of the last 50 years," former Commissioner Fay Vincent said. "He changed not just the sport but the business of the sport permanently, and he truly emancipated the baseball player -- and in the process all professional athletes. Prior to his time, they had few rights; at the moment, they control the games."
MLB's revenue has grown from $50 million in 1967 to $7.5 billion this year. At his last public speaking engagement, a discussion at New York University School of Law in April marking the 40th anniversary of the first baseball strike, Miller maintained free agency and resulting fan interest contributed to the revenue increase.
"I never before saw such a win-win situation my life, where everybody involved in Major League Baseball, both sides of the equation, still continue to set records in terms of revenue and profits and salaries and benefits," Miller said. "You would think that it was impossible to do that. But it is possible, and it is an amazing story how under those circumstances, there can be both management and labor really winning."
Miller, who retired and became a consultant to the union in 1982, led the first walkout in the game's history 10 years earlier. On April 5, 1972, signs posted at major league parks simply said: "No Game Today." The strike, which lasted 13 days, was followed by a walkout during spring training in 1976 and a midseason job action that darkened the stadiums for seven weeks in 1981.
Baseball had eight work stoppages through 1995 but has labor peace since then. Meanwhile, labor turmoil has engulfed the other major U.S. pro leagues.
"Marvin exemplified guts, tenacity and an undying love for the players he represented," NFL players' union head DeMaurice Smith said. "He was a mentor to me, and we spoke often and at length. His most powerful message was that players would remain unified during labor strife if they remembered the sacrifices made by previous generations."
Slightly built and silver-haired with a thick, dark mustache, Miller trained as an economist and was anything but passive in his dealings with baseball owners.
"Marvin Miller was a highly accomplished executive and a very influential figure in baseball history," Commissioner Bud Selig said in a statement. "He made a distinct impact on this sport, which is reflected in the state of the game today, and surely the major league players of the last half-century have greatly benefited from his contributions."
Former Commissioner Peter Ueberroth said Miller should be inducted into baseball's Hall of Fame "without question."
"He changed the game of baseball," Ueberroth said. "He was very tough, but he was very fair in the end."
Miller's ascension to the top echelon among sports labor leaders was by no means free from controversy among those he represented. Players from the Los Angeles Dodgers, Atlanta Braves, California Angels and San Francisco Giants opposed his appointment as successor to Milwaukee Circuit Court Judge Robert Cannon, who had counseled them on a part-time but unpaid basis.
Miller overcame the opposition, however, due in part to his personality.
"Some of the player representatives were leery about picking a union man," Hall of Fame pitcher and former U.S. Senator Jim Bunning, a member of the screening committee that recommended Miller, remembered in a 1974 interview. "But he was very articulate ... not the cigar-chewing type some of the guys expected."
Miller recalled that owners "passed the word that if I were selected, goon squads would take over the game. They suggested racketeers and gangsters would swallow baseball. The players expected a 'dese, dem and dose' guy. The best thing I had going for me was owner propaganda."
When Miller made a tour of spring training camps in 1966, seeking support from the players, some coaches and managers who were members of the association at that time heckled him and disrupted his sessions.
"A lot of players figured that anyone the owners disliked that much couldn't be all bad," former club owner Bill Veeck said.
Miller was elected by a vote of 489-136 on April 15, 1966. Baseball had entered a new era, one in which its owners would have to bargain with a union professional.
The owners made it clear that Miller's election would bring an end to their financial contributions to the association, which had been formed in 1954 because players were disenchanted with the way their pension plan was being administered. Miller insisted he would have asked for the change in any event.
"I told them that if they wanted to make any real headway, they'd have to adopt an independent stance," Miller said.
The players' association consisted of a $5,400 kitty and battered file cabinet when Miller took the reins shortly after calling baseball's minimum salary of $7,000 "unreasonably low."
Today the biggest stars earn up to $32 million a season, the average salary is more than $3 million and the major league minimum is $480,000
Baseball salaries increased by nearly 500 percent under Miller's leadership, more than three times the rate at which manufacturing workers' wages rose.
Yet baseball's Hall of Fame repeatedly refused to vote him in.
"I and the union of players have received far more support, publicity, and appreciation from countless fans, former players, writers, scholars, experts in labor management relations, than if the Hall had not embarked on its futile and fraudulent attempt to rewrite history," Miller said after falling one vote shy in December 2010. "It is an amusing anomaly that the Hall of Fame has made me famous by keeping me out."
Miller's legacy -- free agency -- represented the most significant off-the-field change in the game's history. He viewed the reserve clause that bound a player to the team holding his contract as little more than 20th century slavery.
"I had seen some documents in my life, but none like that," Miller said in 1966 after reading a Uniform Player's Contract.
He decided the reserve clause had to be tested. It was, when outfielder Curt Flood, traded by St. Louis, refused to report to Philadelphia in 1969.
Three years later, the U.S. Supreme Court upheld the validity of the reserve clause by a 5-3 vote, keeping intact baseball's antitrust exemption.
Still, the die was cast when Justice Harry Blackmun, in his majority opinion, wrote that baseball's exemption from ordinary law was an "aberration" that had survived since the court ruled for the game in 1922. The reserve clause would not survive its next test.
In 1975, Los Angeles pitcher Andy Messersmith and Montreal pitcher Dave McNally, with Miller orchestrating the attack, did not sign contracts and their teams invoked baseball's so-called renewal clause. That gave the team the right to renew a player's contract without his approval.
Players argued there could only be a one-time renewal, while management said the renewal could be invoked in perpetuity.
Arbitrator Peter Seitz sided with the players on Dec. 23, 1975. The owners appealed his decision in federal court, saying the reserve system was not subject to arbitration. Two months later, U.S. District Judge John Watkins Oliver upheld Seitz's decision, and teams then went to the 8th U.S. Circuit Court of Appeals, which also upheld Seitz.
In negotiations later that year, the sides agreed to a labor contract that allowed players with six years of major league service to become free agents. Free agency became a reality nearly 100 years after the first players were put under contract.
"Marvin possessed a combination of integrity, intelligence, eloquence, courage and grace that is simply unmatched in my experience," said Donald Fehr, a successor to Miller as union head.
"Without question, Marvin had more positive influence on Major League Baseball than any other person in the last half of the 20th century."
Miller was born in New York, the son of a salesman in the heavily organized garment district. His mother was a school teacher. He studied economics at Miami (Ohio) University and New York University.
He entered the labor field in 1950 as an associate director of research for the United Steelworkers Union. In 1960, he was promoted to assistant to union president David McDonald. When McDonald lost a hotly contested election to I.W. Abel, Miller began looking for a new job.
He and his wife Terry, the parents of two grown children, carefully considered their options, and Miller accepted the directorship of the players' association even though he had some reservations at the time. In fact, he thought his union image had "put some of them off."
"I was surprised when they called me back and asked me to stand for election," Miller said.
In the end, Miller's reputation as a hard worker won over the players, many of whom considered him the consummate professional.
"Baseball is my racket," Pete Rose said. "When it comes to negotiating ... that's Marvin's racket."
Terry Miller died in October 2009. In addition to his daughter, Miller is survived by son Peter Miller and grandson Neil Satoru Miller. Susan Miller said her father, like her mother, wanted his body donated to research at Mount Sinai Hospital. She said the family had not decided whether there would be a service.