[6] On March 24, 2024, Sullivan made his professional debut, coming on in the 56th minute in an MLS Next Pro match for Philadelphia Union II.

[10][11] Sullivan and his family confirmed to ESPN that the contract has a clause that calls for a transfer to Manchester City once he turns 18.

His father, Brendan, played for five clubs over a six-year professional career in the A-League, now known as the USL Championship, the second division of American soccer.

Prior to that, Brendan Sullivan was an All-Ivy League selection at the University of Pennsylvania (Penn) and before that starred at St. Joseph's Prep in Philadelphia.

[21] His other older brothers, Declan and Ronan, are also soccer players, with both currently attending YSC Academy and playing for MLS NEXT affiliate FC DELCO.

[22] Cavan's older cousin is Chris Albright, an American international who played two seasons for the Union, and his grandfather is Larry Sullivan, who served as the head coach at Villanova from 1991 to 2007.