At Rockport-Fulton High School, Nguyen played middle linebacker and handled punting duties.
Nguyen was recruited and received scholarship offers from Michigan, UCLA, Notre Dame, Texas, and Florida.
That same year, Texas A&M won the Big 12 championship game against Kansas State which is to date their last conference title.
In 2002, while playing against the Houston Texans in the season opener, he suffered a broken wrist that forced him to miss the next eight games.
When head coach Bill Parcells arrived in 2003, he was critical of the linebackers in the Cowboys roster, joking publicly: "If this were the circus, we could fit them all into one of those Volkswagens that 10 clowns climb out of."
In 2003, with Nguyen leading the team in tackles, the Cowboys were the second-most effective defense in the NFL and he was selected second-team All-Pro by the Associated Press.
In 2004, Parcells implemented his preferred 3–4 defense and Nguyen repeated as the team's leading tackler, but the additional hits he received in this scheme started to affect his health.
He returned as a nickel linebacker and played in four more games, before being placed on the injured reserve list on November 28, after the Thanksgiving Day overtime loss against the Denver Broncos.
Nguyen officially retired from the NFL on March 3, 2006, after a neck injury and knee problems, which hindered his performance, failed to improve.
[4] As of November 2010, Dat Nguyen currently ranks 10th all-time in Cowboys recorded history for career total tackles.
The resurgence of the Texas A&M defense to its former glory as the "Wrecking Crew" and particularly the outstanding play of the linebacker corps has been cited as a major reason for the team's 2010 season success.
At the conclusion of the 2011 season, Nguyen chose to leave Texas A&M, telling the Houston Chronicle's Brent Zwerneman that there was "no chance" of him being retained on Kevin Sumlin's staff.
[12] In March 2016, Nguyen became an owner/operator of a Chick-fil-A franchise located at Montgomery Plaza in Fort Worth, Texas.