[2] All players, managers, coaches, and athletic trainers who hold or have held a signed contract with a Major League club are eligible for membership in the Association.

On September 9, 2022, MLB voluntarily recognized the MLBPA as the union for over 5,500 minor league baseball players playing rookie ball to Triple-A.

Through the Players Trust, Major Leaguers contribute their time, money and fame to call attention to important issues affecting those in need and to help encourage others to get involved in their own communities.

That year the newly recognized union hired Marvin Miller from the United Steel Workers of America to head the organization, serving as executive director until 1983.

In 1968, Miller negotiated the first collective bargaining agreement (CBA) with the team owners, which raised the minimum salary from $6,000 to $10,000 per year.

In 1974, when Oakland owner Charlie Finley failed to make a $50,000 payment into an insurance annuity as called for in Catfish Hunter's contract, the MLBPA took the case to arbitration.

In the late 1980s and early 1990s the MLBPA filed collusion charges, arguing that team owners had violated the collective bargaining agreement in the 1985–1987 seasons.

In 1987, arbitrator Tom Roberts found that owners had violated the terms of the Basic Agreement, with players later being awarded $10.5 million.

In 1989, arbitrator George Nicolau found that owners had violated the Basic Agreement on the second grievance, with players awarded $38 million.

[24][25] In 1968, the Major League Baseball Players Association negotiated the first-ever Collective Bargaining Agreement (CBA) in professional sports.

[29] The terms of this joint policy cover four primary areas: Treatment & Intervention; Investigations; Discipline; and Training, Education & Resources.

In June 2016, executive director Tony Clark and MLB commissioner Rob Manfred, along with Curtis Granderson, Andrew McCutchen, Marquis Grissom, and Ken Griffey Jr., announced major initiatives within youth baseball in a press conference held at Citi Field.

On top of jointly donating over $2 million several youth-focused initiatives supported by current and former Major League player, other major initiatives included financial contributions to youth baseball projects and the creation of a partnership with Positive Coaching Alliance for the training of coaches and administrators from the Reviving Baseball in Inner Cities program.