McMillian began playing basketball in junior high school and practiced on the playgrounds of New York City.[1] His older brother arranged for him to attend Storm King School in upstate New York and funded his education.[1][2]
McMillian started his college basketball career with the Loyola Marymount Lions where he played at the guard, small forward and center positions.[2] He transferred to the Long Beach State 49ers and had to sit out the 1975–76 season as a transfer student.[2] McMillian became eligible to play during the 1976–77 season.[3] Playing as a small forward for the 49ers,[2] he averaged 15.7 points per game and was selected as the PCAA Player of the Year in 1977.[4]
McMillian was selected by the New York Knicks in the third round of the 1977 NBA draft.[5] He was invited to the Knicks' rookie camp in 1977,[6] and was one of six players there to receive an invite to training camp.[7] McMillian was unable to agree on contractual terms and instead played in France during the 1977–78 season.[8]
McMillian played in a Long Beach State alumni game in 1985.[9]