He played college football for the Butte Roadrunners and the Sonoma State Cossacks, and was selected by the Cowboys in the second round of the 1994 NFL draft.

[1][2][3][4] Spending his first 12 seasons with the Cowboys, Allen earned ten Pro Bowl selections and six first-team All-Pro honors.

[5] Allen grew up in Compton, California, and had a troubled childhood, including contracting meningitis and almost dying at six weeks old, as well as being stabbed 12 times in the head, shoulder, and neck by a young neighbor while trying to protect his brother at the age of 10.

During the season, he tied Burton Lawless in 1975 and Kevin Gogan in 1987, for the most starts on the offensive line as a rookie in club history at the time; Flozell Adams broke the record in 1998.

Allen helped Dallas establish a then team record by allowing just 20 sacks totaling just 93 yards (fewest in the NFL) while earning all-rookie honors.

[citation needed] Allen was forced into a starting spot just four games into his rookie season when Mark Tuinei suffered back spasms on the road against the Washington Redskins.

[4][11] The game's announcers (Al Michaels, Frank Gifford, and Dan Dierdorf) talked more about Allen's amazing feat than the actual interception.

He was one of a club record four Dallas offensive linemen named to the Pro Bowl, with Ray Donaldson, Nate Newton, and Mark Tuinei being the others.

The Dallas offensive line led the league by allowing just 19 sacks, one shy of the team record set the previous year.

Allen returned to the starting lineup following the bye week against the Chicago Bears on September 28, but was forced to leave in the second quarter with insufficient strength in his left leg to block effectively.

He was back in the starting lineup the following week at the Giants, where he was forced to move to left tackle after the loss of Tuinei during a game at Washington on October 13.

He earned recognition as part of an offensive line that allowed just 19 sacks for 110 yards in 493 pass plays for a season, the fewest in the NFL.

In November, he faced four of the NFC's top defensive ends in Hugh Douglas, Chad Bratzke, Simeon Rice, and John Randle.

In 1999, despite starting in his third offensive line position in as many years and missing five games due to injury, Allen was selected to his fifth consecutive Pro Bowl while earning consensus All-Pro honors at guard.

He helped lead the way as the Cowboys gained 541 total yards while giving up only one sack in 50 pass plays in his first career start at left guard at Washington on September 12.

Allen helped the Cowboys running backs record 149 yards before leaving the game in the third quarter with a sprained medial collateral ligament (MCL) in his right knee against the Packers on November 14.

In the NFC Wild Card Playoff Game in Minnesota on January 9, he opened holes for Smith to rush for 99 yards, including a Dallas postseason record 65-yarder.

His blocking helped limit the Cardinals to one sack while protecting Randall Cunningham as he completed 24-of-34 passes for 243 yards and three touchdowns on September 10.

He was also part of an offensive line that helped Smith rush for 150 yards and a touchdown against the Redskins and the NFL's fourth-ranked defense on December 10.

He played through off-season surgery and a nagging early-season ankle sprain that limited him to five starts on the season between left guard and right tackle.

Due to his off-season rotator cuff surgery on his left shoulder, and was limited in training camp and played in just the final two preseason games.

In 2003, Allen returned after missing most of the 2002 season with a sprained left ankle that required off-season surgery to remove bone spurs.

Despite missing parts of four games with injuries, he returned and was honored for play with eighth Pro Bowl selection at guard.

He played at the New York Giants on September 15, and helped protect Quincy Carter, allowing him to throw for 321 yards in leading Dallas to a come-from-behind overtime win.

He suffered a sprained left knee in the second quarter against the Cardinals on October 5, but returned in the second half to help Dallas total 365 yards of offense.

His run blocking allowed Julius Jones to rush for 194 yards, the fourth-best performance in franchise history in Carolina on Christmas Eve.

He was voted to his 11th career Pro Bowl after blocking for RB Frank Gore's franchise record 1,695 rushing yards on the season.

The entire offensive line was awarded game balls by Head Coach Mike Nolan, in part for their job blocking for the running back, who rushed for 198 yards against the Lions on November 12.

He started at left guard against the Seahawks on November 19, and played with an offensive line that blocked for Gore's single-game franchise record 212 rushing yards.

During the half-time show of the Cowboys-Seahawks game, November 6, 2011, Allen, Drew Pearson, and Charles Haley were inducted into the Dallas Cowboys Ring of Honor.