The sport's "reserve clause" was bolstered by a 1922 U.S. Supreme Court ruling that baseball was not a business and therefore not subject to federal antitrust laws. Baseball was — and still is — the only sport to enjoy such an exemption.
The new union boss began by negotiating a raise in minimum salary — from $6,000 to $10,000 a season — and persuading owners to accept arbitration for disputes, a victory that would prove significant.
Occasionally portrayed as hard-edged, Miller more often relied on persistence and compromise. His late wife, Terry, told The Times: "One of the things I get most impatient with Marvin about is his infinite patience." He was also matched against baseball commissioners — first Spike Eckert, then Bowie Kuhn — perceived as less-skilled negotiators.
With salary issues resolved, Miller revisited players, preparing his constituency for a battle over the reserve clause that would be waged on several fronts.
In 1970, St. Louis Cardinals outfielder Curt Flood challenged the clause in court. Miller did not expect success — the U.S. Supreme Court eventually ruled against Flood — but considered it a first step and followed up with a 13-day strike in 1972.
Then, in 1974, Oakland A's owner Charles O. Finley neglected to pay an agreed-upon insurance policy for Jim "Catfish" Hunter. The ace pitcher turned to arbitration — the process Miller had won for players — and became the game's first free agent, signing with the New York Yankees for $3.75 million over five years.
The final step came a year later, by way of an overlooked phrase in the standard contract. By Miller's reading, it stated that if a player's contract expired and he did not sign a new one, his team could keep him for one more season under the old terms. The union boss interpreted this to mean the player then became a free agent.
In 1975, Andy Messersmith of the Dodgers and Dave McNally of the Montreal Expos tested the theory, playing unsigned. They subsequently won in arbitration, striking down the reserve clause. Baseball had entered a new age.
"I don't think it would have happened without him," said Spencer Waller, co-author of "Baseball and the American Legal Mind." "When [baseball] caved, that paved the way for all other sports."
The NBA quickly adopted free agency, with the NFL following later. Miller led his players through one more strike in 1981 — lasting 50 days — before stepping down in 1982 to become a consultant.
Even in semi-retirement, he remained a lightning rod for criticism as fans grew increasingly disenchanted with skyrocketing player salaries. Upon the publication of his 1991 book, "A Whole Different Ball Game: The Inside Story of Baseball's New Deal," which characterized owners as boorish if not corrupt, critics labeled him as conceited.
Yet, the Sporting News ranked Miller as the fifth most-influential figure in 20th century sports and a new generation of players continued to benefit from his efforts. The league's minimum salary is now $480,000 — 80 times the minimum pay when Miller took over the union.
"He made a distinct impact on the sport, which is reflected in the state of the game today," Commissioner Bud Selig said.
One place Miller has not earned respect is in baseball's Hall of Fame. While former players such as Aaron and Joe Morgan have called for his election — pitcher Nolan Ryan even thanked him during a 1999 Hall of Fame acceptance speech — Miller has never garnered the necessary votes.
In a 2004 interview at his home on New York's Upper East Side, the former union leader — who is survived by son Peter, daughter Susan and a grandson — smiled at the idea of receiving support from an electorate that includes team and league executives. He did not expect a groundswell from fans, either.
"Sure, it would mean a lot to me, but I never was holding my breath," he said. "I've been a trade unionist all my life and, as such, you learn early that you're not to court popularity with either the management or the public."