[3] Also a standout athlete, DeCastro competed for the school's track and field team as a shot putter.

Afterward, he decided to forgo his final season of college eligibility and enter the NFL Draft.

[10][11][12] He attended the NFL Combine and was said to have "excellent movement skills" and was able to complete all the drills and positional workouts.

Although he participated Stanford's pro day, he decided to only do positional drills, as he was satisfied with his combine numbers.

[18] He entered training camp competing for a starting guard position with veterans Willie Colon, Ramon Foster, and Trai Essex.

With the departure of Willie Colon and Trai Essex, DeCastro entered the season as the Pittsburgh Steelers' de facto starter at right guard.

During the tenth play of the game, DeCastro accidentally whiffed during a cut block and fell down onto the back of Maurkice Pouncey's right knee.

[21] He was replaced by Guy Whimper during the Steelers' Week 9 matchup with the New England Patriots after suffering an ankle injury.

On January 3, 2014, he played in his first career postseason game as the Steelers lost in the AFC Wildcard to the Baltimore Ravens.

[24] On April 9, 2015, the Pittsburgh Steelers exercised the fifth-year option on DeCastro's rookie contract, paying him a salary of $8.07 million for 2016.

[18] In his fourth season with the Steelers in 2015, DeCastro started in all 16 regular-season games and was elected to his first Pro Bowl.

[27] He was ranked the ninth best offensive guard by Sports Illustrated after he surrendered only 1.5 sacks in 590 pass blocking attempts and was flagged for three penalties (all false starts) all season.

[32] On December 19, 2017, DeCastro was named to his third-straight Pro Bowl along with fellow Steeler offensive linemen Alejandro Villanueva and Maurkice Pouncey.

[35] In week 1 against the Cleveland Browns, DeCastro fractured his right hand and was forced to miss the next two games against the Kansas City Chiefs and Tampa Bay Buccaneers.

Afterwards, DeCastro grabbed Garrett, pushed him onto the ground, and laid on top of him to prevent an even larger fight from escalating.