Castillo earned a scholarship worth $500 to attend Texas A&I after spending a semester at Monterrey Tech. He played college football while enrolled.
Professional career
Castillo played for the San Antonio Gunslingers of the USFL from 1984–1985, mainly on special teams. In 1984, Castillo saw action in six games, making four tackles and three assists. In 1985, Castillo played in seven games, making eight tackles and registering three assists on a 5–13 club.
The Philadelphia Eagles hired Castillo as an offensive assistant in 1995 under Ray Rhodes. In 1996, the Eagles drafted Jermane Mayberry, an offensive lineman Castillo coached at Texas A&M University–Kingsville, in the first round of the 1996 NFL Draft. Castillo was promoted to tight ends coach in 1997, and switched to coaching the offensive line in 1998. When Andy Reid was hired as the head coach of the Eagles in 1999, he retained Castillo on the coaching staff. Mayberry earned a Pro Bowl berth in 2002, and said Castillo "molded me into the player I became." Castillo coached the offensive line for thirteen seasons, from 1998–2010. Castillo became the defensive coordinator for the Eagles following the firing of Sean McDermott on February 2, 2011. The hiring was met with surprise by players, fans, and members of the media primarily because Castillo had not coached the defensive side of the ball since he was at Kingsville in 1989. After a tumultuous tenure, Castillo was fired on October 16, 2012. He was replaced by Todd Bowles, the team's secondary coach and former interim head coach of the Miami Dolphins.
On January 21, 2013, Castillo was hired as a consultant by the Baltimore Ravens. At the time of the hiring, the Ravens were preparing to play in Super Bowl XLVII. Castillo would officially join the coaching staff for the 2013 season as the run-game coordinator and held the job for one season, before serving as the offensive line coach from 2014 to 2016.
In 2017, Castillo was hired by the Buffalo Bills to become the offensive line coach and run-game coordinator under new head coach Sean McDermott. He served two seasons with the Bills before being dismissed following the 2018 season.
Michigan
Castillo joined the Michigan Wolverines coaching staff as an offensive analyst for the 2019 season. As part of his duties, Castillo worked with Michigan offensive line coach Ed Warinner.
Chicago Bears
On January 5, 2020, the Chicago Bears hired Castillo as offensive line coach. The move reunited him with head coach Matt Nagy, whom he worked with in Philadelphia.
Personal life
Castillo is married; he and his wife, Zaida, have four sons. On August 17, 1998, Castillo fractured his left tibial plateau after he was hit by a utility truck outside of Veterans Stadium. Even though he was on crutches, he still coached practice the following day. In 2002, Castillo and his wife were invited to a Cinco de Mayo celebration by President George W. Bush at the White House. Port Isabel, Texas declared July 4, 2009 to be "Juan Castillo Day" and presented Castillo with a key to the city.
