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. He played in the team's first preseason game, being successful on both of his field goal attempts and averaging 66.0 yards on two kickoffs. Unable to unseat the incumbent, Matt Bryant, Castillo was released shortly after that game on August 9, 2014.
On August 28, 2015, Castillo signed with the Winnipeg Blue Bombers to a practice roster agreement. 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. He was a perfect 5-for-5 in field goal attempts in his debut and remained the team's placekicker for the last four games of the season, finishing with 10 field goals from 13 attempts. In the following off-season, the Blue Bombers moved on from Hajrullahu and signed Justin Medlock to compete with Castillo. As the most accurate placekicker in CFL history, Medlock won the starting job and Castillo began the season on the injured list. He did not play in a regular season game in 2016 and was eventually released on September 2, 2016.
On September 11, 2016, Castillo signed with the Ottawa Redblacks and replaced the injured Zackary Medeiros at punter. Castillo punted in two games, recording 13 punts for a 45.2-yard average, but was released on September 26, 2016.
On May 28, 2017, Castillo signed with the Hamilton Tiger-Cats to compete for the kicker position vacated by Brett Maher. He won all three kicking duties following training camp and had a career year with the Tiger-Cats. He made 29 of 34 field goals, 20 of 21 converts, and had 93 punts for a 45.1-yard average in 14 games. However, on October 6, 2017, Castillo suffered a season-ending ACL injury while attempting to make a tackle after his missed field goal attempt. He was released in the following off-season on February 24, 2018.
Ottawa Redblacks (II)
Castillo signed again with the Ottawa Redblacks on April 9, 2018 to try out for a vacant kicker position, soon after his recovery from his ACL injury, but was unable to secure a position with the team. He remained unsigned for the 2018 CFL season and did not play that year.
Castillo was one of the first players to sign with the San Antonio Commanders of the upstart Alliance of American Football when his signing was announced on August 6, 2018. He did not play in the Spring-based league as he was released on January 19, 2019.
BC Lions
On May 26, 2019, Castillo signed with the BC Lions and began the season with all three kicking duties. He started the season making all ten of his field goal attempts before missing a potential game-winning 42-yard field goal try in the July 6, 2019 game against the Toronto Argonauts. 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. 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.
On November 22, 2019, Castillo was drafted by the Houston Roughnecks in the 2020 XFL Supplemental Draft. He played in five games and was successful on five field goals. He had his contract terminated when the league suspended operations on April 10, 2020.
BC Lions (II)
On April 19, 2020, it was reported that Castillo had re-signed with the BC Lions. On April 20, 2020, the club officially announced that he had signed a two-year contract to re-join the team.
