[4] As a freshman at West Virginia, Mazzulla helped the team win the 2007 National Invitation Tournament under coach John Beilein.

[6] In April 2009, Mazzulla was arrested for domestic battery at a bar in Morgantown, West Virginia, and was suspended by coach Bob Huggins.

[7] As a redshirt junior, Mazzulla was named a captain and helped West Virginia reach the 2010 Final Four, where the Mountaineers lost to eventual champion Duke.

[11] Shortly after graduating from college, Mazzulla was offered a coaching job at Nova Southeastern but turned it down to pursue professional playing opportunities.

[12] Mazzulla joined Glenville State as an assistant in September 2011 after he was unable to find any professional playing opportunities.

[10] During his second season, Mazzulla led the team to a 22–9 record and an appearance in the 2019 NCAA Division II tournament, where they lost in the first round to Mercyhurst, 63–60, in overtime.

[15][16] On September 22, 2022, just days before the beginning of training camp, Mazzulla was named interim head coach for the Celtics after Ime Udoka was suspended for the entire 2022–23 season due to violating team policies.

[17][18] On December 1, Mazzulla was named Eastern Conference Coach of the Month for October and November after the Celtics began the season with a league-best 18–4 record.

[26] Mazzulla was retained as head coach for the 2023–24 season and received the endorsement of President of Basketball Operations Brad Stevens, who called him "a terrific leader" and "accountable.

"[27][28] During the season, Mazzulla earned two Eastern Conference Coach of the Month awards, one in December and another in March.

[31][32] The Celtics went on to beat the Miami Heat and Cleveland Cavaliers in five games during the first round and Eastern Conference Semifinals, respectively.