As a player, he threw and batted left-handed, stood 5 feet 11 inches (1.80 m) tall, and weighed 172 pounds (78 kg).

[2] In 1994, McMillon played for the Kane County Cougars and was selected as a starter for the Midwest League all-star game.

[5] McMillon advanced to Triple-A in 1996; playing for the Charlotte Knights, he was named International League rookie of the year.

[7] McMillon also played in a total of 992 minor league games during parts of 11 seasons, with a .304 batting average, 127 home runs, and 610 RBIs.

[9] After finishing one game under .500 in 2012, he was retained as Salem's manager for the 2013 season[10] and led his team to the Carolina League championship.

Salem won the second half Southern Division title, and then bested the Myrtle Beach Pelicans and the Potomac Nationals in the playoffs.

[11] On December 18, 2013, McMillon was named manager of the Portland Sea Dogs, the Red Sox' affiliate in the Double-A Eastern League and the team that he had played for (with the Marlins) in 1995.

[12] His managerial debut with the 2014 Sea Dogs produced a first-place finish in the Eastern League's Northern Division with an 88–54 record.

[13] During the season, his club included top prospects such as Mookie Betts, Blake Swihart, Henry Owens, Deven Marrero, Brian Johnson, Eduardo Rodríguez and Travis Shaw; all but Rodríguez were promoted to higher levels by the time of the Eastern League playoffs, when Portland fell to the Binghamton Mets in the first round.

McMillon spent 2016 to 2018 as the roving minor league outfield and base running coordinator in the Red Sox' farm system.