McMillan attended Cloverdale (CA) High School, where he led his team to two California Class A Division III state titles during his junior and senior seasons. He scored 2,310 points during his prep career, which was fifth-best in California high school history. He was named to the Converse, Parade and McDonald's All-American teams following his senior season in 1984.

Kevin O'Neill recruited McMillan and convinced him to attend the University of Arizona. Craig was a four-year letter winner from 1985-88 and left as the school's 12th all-time leading scorer (1,166 points). He averaged 9 points per game and started 118 of 130 games during his career. He was nicknamed “McClutch” for the many game-winning shots he made for the Wildcats. McMillan was the starting guard on the 1988 Arizona Wildcat squad that made it to the Final Four and is the only starter from that team who did not go on to play professionally. Some of McMillan's teammates from that squad included Steve Kerr, Anthony Cook, Sean Elliot, Tom Tolbert, Jud Buechler, and Kenny Lofton. McMillan graduated from Arizona with a bachelor of arts degree in economics with a minor in sociology.

McMillan came to Marquette from Arizona with Kevin O'Neill, serving as a graduate assistant coach from 1989-1991. When Randy Brown left to take the head coaching position at Stetson, McMillan was promoted to the third assistant coach position. When O'Neill left Marquette, McMillan went with him to Tennessee. McMillan spent a total of eight years working under O'Neill, before pursuing coaching opportunities in the Middle East.

McMillan coached professional teams in Kuwait and Lebanon for four seasons, before returning to his northern California roots. The 2007-08 season marks his eighth as the head coach at Santa Rosa Junior College in Santa Rosa, California.