His family said Miller died Tuesday at his home in New York. He had been diagnosed with liver cancer earlier this year.
Miller helped major league players create their union in 1966 and served as the head of the MLBPA until 1982.
"All players -- past, present and future -- owe a debt of gratitude to Marvin and his influence transcends baseball," current MLBPA leader Michael Weiner said in a statement Tuesday.
"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."
Miller led a committee of players that negotiated the first collective bargaining agreement in 1968. The agreement raised the minimum salary in baseball from $6,000 -- the level at which it had been stuck for two decades -- to $10,000 and set the tone for future advances.
One of those for the players was the advent of free agency and the end of the reserve clause, which bound players to a team at the team's will. In 1975, pitchers Andy Messersmith and Dave McNally challenged the reserve clause in court, where a legal victory ended the practice, basically allowing players to open bidding for their talents.
Miller led the players through strikes in 1972, 1980 and 1981. There were also owner lockouts in 1973 and 1976.
"Marvin Miller was a highly accomplished executive and a very influential figure in baseball history," MLB Commissioner Bud Selig said in a statement Tuesday. "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."