Castillo was undrafted in the 2014 NFL draft and signed as a free agent placekicker with the Atlanta Falcons of the National Football League on June 12, 2014.

[3] After the incumbent Winnipeg kicker, Lirim Hajrullahu, missed four of five field goal attempts in a week 15 game against the Edmonton Eskimos, Castillo replaced him and made his professional regular season debut on October 10, 2015, against the BC Lions.

As the most accurate placekicker in CFL history, Medlock won the starting job and Castillo began the season on the injured list.

[18] However, because the kick had enough distance, the returner, Chris Rainey, stepped out of bounds at the end line and Castillo had the first game-winning last-play rouge since October 14, 2002.

[19] He finished the season connecting on 41 field goals out of 45 attempts for a league-leading 91.1% success rate and was named a CFL All-Star.

[23] After the CFL canceled the 2020 season due to the COVID-19 pandemic, Castillo chose to opt-out of his contract with the Lions on August 28, 2020.

[25] He was elevated to the active roster on October 24 for the team's Week 7 game against the Buffalo Bills with Sam Ficken out with a groin injury.

[31] On October 19, 2021, the Blue Bombers acquired Castillo's playing rights via trade from the BC Lions, in exchange for a conditional 4th round pick in the 2022 CFL Draft.

[33] The Lions had maintained Castillo's rights after he opted out of his two-year contract on August 28, 2020, to pursue opportunities in the NFL.

Castillo's abilities were not required in the CFL West Division final taking place at home in stormy conditions as the bombers scored three touchdowns to get to the 108th Grey Cup.