[3] Castro made his professional debut on June 16, 2016, scoring a four-round unanimous decision (UD) victory against Tony Green at the Celebrity Theatre in Phoenix, Arizona.
[4] After compiling a record of 19–0 (8 KOs), he returned to the Celebrity Theatre to face Alexis Santiago for the vacant WBC–USNBC super bantamweight title on February 24, 2018.
[5][6] In June of that year, it was announced that Castro had signed a multi-year contract with Bob Arum's Top Rank promotional company.
[11] Castro's next fight came against former two-weight interim world champion Óscar Escandón on August 21, 2021 at the T-Mobile Arena in Paradise, Nevada.
In a bout that served as part of the undercard for Manny Pacquiao vs. Yordenis Ugás, Castro scored knockdowns in rounds seven and ten, the latter of which promoted the referee to call a halt to the contest at 1 minute 8 seconds into the round, awarding Castro the vacant WBC Continental Americas featherweight title victory via tenth-round knockout (KO).