Freeney was born in Hartford, Connecticut. He attended Bloomfield High School in Bloomfield, Connecticut. Freeney was a four-sport letterman, earning four letters in baseball in which he was coached by Alphonso Ford; four in basketball; three in football, in which he played both ways; and one in soccer, in which he played goalie in his freshman year before switching over to football. Freeney currently holds the record for sacks at his high school and most sacks in a high school career in the Connecticut record book. Bloomfield High retired his No. 44 football jersey. During his youth, Freeney idolized New York Giants linebacker Lawrence Taylor, whom he later met at a charity golf tournament after turning pro.
Freeney received an athletic scholarship to attend Syracuse University, where he played for the Syracuse Orange football team from 1998 to 2001. A two-year starter for the Orangemen, he set a school record with 17.5 sacks in his senior season and his 34 career sacks rank second in school history to Tim Green (45.5). Freeney was the school's premier pass rusher, and once had a string of 17 consecutive games with at least one sack. Against Virginia Tech, Freeney sacked elusive Hokies quarterback Michael Vick 4.5 times in one game.
He finished his college career with 104 tackles (68 unassisted), 34 quarterback sacks, 51 tackles for a loss, and 43 quarterback pressures. He was a first-team All-Big East Conference selection in 2000 and 2001, and was recognized as a unanimous first-team All-American following his senior season in 2001.
While attending Syracuse at a then 255-pounds, Freeney was clocked at 4.40 second 40-yard dash and recorded 40-inch vertical jump. This is one of the fastest times ever recorded by a defensive lineman.
Dwight still returns to Syracuse for his summer workouts, and serves as mentor to Syracuse players, including former walk-on Josh Arrington from the 2006-2008 season.
When drafted by Indianapolis at 270 lbs Freeney was clocked at 4.48 second 40 yard dash and the same 40 inch vertical jump.
In 2004, Freeney's third season, he led the NFL with 16 sacks. At the end of his third season, Freeney's season marked him as the 3rd fastest player to achieve 40 sacks. He developed a spin move which became his trade mark pass rush move.
On February 19, 2007, the Colts placed the franchise tag on Freeney following the expiration of his rookie contract. This move allowed Bill Polian and the Colts front office time to work on a long term contract. On July 13, 2007 Freeney signed a six-year, $72 million contract with $30 million in guarantees making Freeney one of the highest paid defensive players in the NFL.
Freeney was fined $20,000 by the NFL for his expletive-laced interview following the end of the Colts 2008-09 playoff campaign which ended with a 23-17 overtime playoff loss to the San Diego Chargers. The NFL cited Freeney for making "inappropriate comments on officiating," according to the Indianapolis Star. Freeney, frustrated by the three defensive penalties incurred as the Chargers made their game-winning drive, told Yahoo! Sports after the game: "Those were the worst [expletive] calls I've seen in a long time ... To have a game of that magnitude taken out of your hands, it's just disgusting. It's not like they made one [expletive] bad call -- it's three calls, in overtime ... They need to start investigating some other [expletive]."
In 2012, Freeney converted from defensive end to outside linebacker under new head coach Chuck Pagano. Due to injury and not adjusting to his position-change well, Freeney struggled and finished the season with only five sacks and 12 tackles.
On February 15, 2013, Freeney was told he would not be re-signed by the Colts. Freeney left as the all-time franchise leader in sacks with 107.5, eventually being surpassed by former teammate Robert Mathis the next season. Mathis would also break Freeney's franchise record of 16 sacks in a season the following season, too.
On May 18, 2013, Freeney signed a two-year deal with the San Diego Chargers. After playing in just four games in 2013 (and registering a career-low 0.5 sacks, Freeney bounced back in 2014 and played in all 16 games and totaled 3.5 sacks.
On March 28, 2012, his financial advisor was arrested and charged with embezzling $2.2 million from Freeney. In 2015, Freeney sued Bank of America for $20 million claiming he trusted the bank's wealth management division with the assets.