Prior to Drexel, he served as the head coach for Chestnut Hill College, Penn State Abington, as well as the USL League Two side, Reading United.
In 1998, Castellanos began his collegiate career at Mercer County Community College.
On March 30, 2004, the Colorado Rapids of Major League Soccer, signed Castellanos.
In August 2006, Castellanos became coach of Penn State Abington men's and women's soccer teams.
USL Premier Development League side Reading United A.C. named Castellanos as the club's head coach on December 28, 2013.