He played college football for the Army Black Knights and fulfilled his service commitment after graduation, where he reached the rank of captain.

After serving three tours of duty in Afghanistan, he signed a contract with the Philadelphia Eagles in 2014, but was waived prior to the season.

Villanueva played college football for the Army Black Knights at several positions, including left tackle, defensive lineman, and wide receiver.

Voted a team captain before his senior year, he reluctantly converted once more to become a 290 pounds (130 kg) wide receiver; a feature story in the Army football program read, "Already touted as the tallest football player in the country, Villanueva completed the transformation from being an offensive lineman for the past two years, to running routes on the field with the starting offense last Saturday night.

[5] Although he went undrafted in the 2010 NFL draft, he received a tryout with the Cincinnati Bengals as a tight end, but did not make the team and went back into military service.

After finishing his last tour with the 75th Ranger Regiment, Villanueva decided to pursue his NFL career again and began working out at Savannah State University.

In April 2014, he was one of 240 prospects invited to the NFL super regional combine in Detroit and met with representatives from the Philadelphia Eagles.

[17] He was able to get reps in training camp and preseason as the second-team swing tackle, after Mike Adams suffered an injury.

The following week, Villanueva received his first career start at offensive tackle since his sophomore year at Army in 2008 and was tasked with blocking Kansas City Chiefs Pro-Bowl defensive end, Tamba Hali.

His run blocking and pass protection greatly improved after Week 7 and he only allowed one sack in the last ten games, helping the Pittsburgh Steelers reach the playoffs.

[23] He finished the season ranking as the 23rd best offensive tackle in the league after receiving an 82.4 overall grade from Pro Football Focus.

[25] On December 19, 2017, Villanueva was named to his first Pro Bowl along with fellow Steeler offensive linemen David DeCastro and Maurkice Pouncey.

[28] On September 24, 2017, prior to a game against the Chicago Bears at Soldier Field, the Steelers did not take the field for the national anthem in order to avoid getting caught up in the controversy related to players kneeling or displaying other signs of racial protest around the NFL started by Colin Kaepernick.

Head coach Mike Tomlin stated a wish to simply play the game and not allow for any show of support one way or the other on the issue.

"[35] At a press conference the day after, he said, "Unfortunately, I threw my teammates under the bus, unintentionally...Every single time I see that picture of me, standing by myself, I feel embarrassed.

"[37] On November 25, 2018, Villanueva caught his first career touchdown pass on a fake field goal from Chris Boswell at the end of the first half in a game against the Denver Broncos.

[39] Cashe was a US Army non-commissioned officer posthumously awarded the Silver Star ( Later upgraded to the Congressional Medal Of Honor) in 2005 for actions he took in Operation Iraqi Freedom to rescue soldiers from a burning vehicle, during which time he sustained burns over 75% of his body and ultimately succumbed to his injuries.

[39] Villanueva stated his actions were intended to support the campaign to upgrade Cashe's award for valor from the Silver Star to the Medal of Honor.

[5] As a result of his actions during this deployment he was awarded a Bronze Star Medal with "V" device for rescuing wounded soldiers while under enemy fire.

[8] On May 9, 2015, Alejandro and Madelyn had a larger ceremony at the Jesus the Divine Word Catholic Church in Huntingtown, Maryland.

After studying part-time for four years, one more than is typical for a student in Tepper's MBA program, Villanueva received his degree in 2019.