Raised in the Landing section of Roxbury, New Jersey, Castanheira played prep soccer at Roxbury High School, leaving after his junior year to join the academy team of Bristol City in 2012, before returning to the United States in 2014.
[2] Castanheira played four years of college soccer at Columbia University, where he made 47 appearances for the Lions and kept 25 shutouts.
[3] While at college, Castanheira also played with Premier Development League side Long Island Rough Riders.
[5] Despite having signed for Atlanta United 2, Castanheira was selected by FC Dallas in the fourth round (88th overall) of the 2019 MLS SuperDraft on January 14, 2019.
[7] On January 27, 2021, Castanheira moved to Fort Lauderdale's parent side Inter Miami in Major League Soccer.