[1] Sullivan retired from playing basketball and joined his alma mater Portland as their director of basketball technology before becoming an assistant coach at Lewis & Clark College, during which he was also an office manager at a construction firm in Vancouver, Washington.

[2] Sullivan joined the San Antonio Spurs front office in 2012 as a video intern on the recommendation of then-Spurs assistant Ime Udoka.

He also worked under Spurs assistant Chip Engelland, considered to be one of the top shooting coaches in the NBA.

[3] Sullivan was one of a number of assistants who joined Budenholzer when the latter was hired as head coach of the Milwaukee Bucks before the 2018–19 NBA season.

[4][5] While in Milwaukee, Sullivan has worked with NBA Most Valuable Player Giannis Antetokounmpo in developing his shooting ability, which has been considered as the main weakness in the Bucks star's basketball game.