He played college football for the USC Trojans where he won the Morris Trophy, recognizing the best offensive and defensive linemen on the West Coast, in 2010.

In 13 seasons with the Cowboys, Smith was an eight-time Pro Bowler, a five-time All-Pro, and was named to the 2010s All-Decade Team.

Smith attended Rancho Verde High School in Moreno Valley, California, where he played on the offensive and defensive line.

His role became even more important after the Cowboys released veteran offensive linemen Marc Colombo, Leonard Davis, Andre Gurode, and Montrae Holland during the preseason.

Smith started every game and earned praise for his play, prompting the media to speculate on a possible move to left tackle in the next season.

On September 12, Smith was fined $15,000 for a touchdown-saving horse-collar tackle he made during the season opener against the New York Giants.

Smith does things to guys—toys with them, humbles them—that you honestly shouldn't be able to do to people in the NFL.Smith signed an eight-year, $109 million contract extension with the Cowboys in July, making him the highest-paid offensive lineman in the league at the time.

[27][28] Smith started all 16 games, helped clear the way for the NFL's fourth leading rusher (Darren McFadden) and earned his third Pro Bowl selection.

[41] Smith's 2017 season was marred by multiple injuries, which included to his knee, back, groin, and hip.

[42] He was placed on injured reserve on December 29, meaning that he would not play in the season finale against the Philadelphia Eagles.

[45] Smith started 13 games at left tackle, missing three with injury, on his way to his sixth straight Pro Bowl.

[54] On October 9, Smith announced that he would forgo the rest of the 2020 season after choosing to have surgery on his neck.

[57] He started in 11 regular season games and the Cowboys' Wild Card Round loss to the San Francisco 49ers.

[66] On March 18, 2024, Smith signed with the New York Jets on a one-year deal worth up to $20 million.