After Week 3, Witten passed Ozzie Newsome for third place all-time in receiving yards among tight ends. In week 8, Witten caught a career-high 18 passes for a career-high 167 yards. This is also a record for receptions by a tight end; the previous record of 15 receptions was set by Kellen Winslow in 1984.

In 2000, Witten accepted a scholarship to the University of Tennessee, with the promise from head coach Phillip Fulmer that he would be played at defensive end. Witten began his first year playing special teams and also saw time as a second-string defensive end.

Witten was selected by the Dallas Cowboys in the third round (69th overall) of the 2003 NFL Draft. Although the Cowboys had a first-round grade on him, when their turn came in the first and second rounds, they selected cornerback Terrence Newman and Al Johnson based on team needs. Undrafted free agent Tony Romo was another rookie who also arrived in Dallas in 2003 and would go on to become Witten’s teammate throughout their careers, as well as his roommate during future team training camps and travel games.

Witten had a breakout season in 2004, leading the NFC with 87 catches, which was also the 11th most in NFL history by a tight end and a Cowboys team record for the position. On November 15, against the Philadelphia Eagles, he had nine receptions for 133 yards and two touchdowns. He was selected to his first Pro Bowl, becoming a part of the Cowboys franchise’s legacy of great tight ends that includes Jim Doran, Lee Folkins, Pettis Norman, Mike Ditka, Billy Joe DuPree, Franklin Clarke, Doug Cosbie and Jay Novacek.

On December 23, against the New Orleans Saints, Witten set the NFL single-season record for receptions by a tight end (103), barely breaking the previous record of 102 receptions, which had been set by Tony Gonzalez in 2004. He extended the record to 110 in the season finale.

Witten finished sixth in the NFL among tight ends with 66 receptions and became the first Cowboys tight end to have at least 65 receptions in consecutive seasons. He had 757 receiving yards and six touchdown receptions in 2005. As a result of his successful season, he was named to his second Pro Bowl.

Witten had a career year in 2007, breaking his own single-season Cowboys tight end record for receptions with 96 and becoming the first franchise tight end to reach 1,000 receiving yards in a season. He became the third tight end in NFL history with 96 or more catches. On December 9 against the Detroit Lions, Witten’s 15 receptions tied an NFL record held by Hall of Famer Kellen Winslow Sr., for most receptions in a game by a tight end in NFL history. In the 14th game of the year, Witten became the first Dallas tight end ever to gain over 1,000 receiving yards in a season. Witten was also one of the NFL-record 13 Cowboys players selected to the Pro Bowl. Additionally, he made the 2007 All-Pro team along with teammates Terrell Owens and DeMarcus Ware. In the Week 9 game on November 4, while playing at Philadelphia, he made a 53-yard reception after losing his helmet. He was named as a First Team All-Pro for the 2007 season.

In 2009, Witten had another Pro Bowl season, making 94 receptions for 1,030 yards and two touchdowns. He was also given the NFL Iron Man Award.

On November 13, 2011, Witten surpassed Ozzie Newsome to become the tight end with the third most receptions in NFL history with 663. Witten finished the season with 79 receptions for 942 receiving yards and five touchdowns playing in all 16 games. He was also ranked No. 75 by his fellow players on the NFL Top 100 Players of 2012.

On August 13, 2012, Witten suffered a lacerated spleen in the preseason opener against the Oakland Raiders and missed the rest of the preseason. There was talk that the seriousness of the injury could keep him out of action for a considerable time.

During the 2015 season, Witten was asked to be more involved in the blocking than usual, because of the team playing with four different starting quarterbacks with varying degrees of knowledge of the offense. He led the Cowboys with 77 receptions for 713 yards and three touchdowns.

On March 28, 2017, Witten signed a four-year contract extension with the Cowboys through the 2021 season.

On April 26, 2018, reports surfaced that Witten was going to retire and accept a position as the lead analyst for ESPN’s Monday Night Football telecasts. A week later, Witten officially announced his retirement and confirmed he would be joining Monday Night Football for the 2018 season.

On February 28, 2019, ESPN announced that Witten will return to the Cowboys on a one-year, $4.5 million deal, and leave his Monday Night Football position at the company. In his return to the gridiron, Witten had three receptions for 15 yards and a receiving touchdown in the 35–17 victory over the New York Giants in the Cowboys’ 2019 regular season opener. Overall, in the 2019 season, Witten recorded 63 receptions for 529 receiving yards and four receiving touchdowns.

On March 25, 2020, Witten signed a one-year contract with the Las Vegas Raiders. He was fined US$15,000 by the NFL on October 5, 2020, for attending a maskless charity event hosted by teammate Darren Waller during the COVID-19 pandemic in violation of the NFL’s COVID-19 protocols for the 2020 season.