Considered a five-star recruit by Rivals.com, Dunlap was listed as the No. 1 weakside defensive end in the nation in 2007. He chose Florida over offers from Clemson, South Carolina, Auburn, and Tennessee.

As a true freshman in 2007, he played in 13 games, recording seven tackles and a quarterback sack. As a sophomore in 2008, Dunlap played in all 14 of the Gators games recording 39 tackles, a team-high 9.5 sacks and three blocked punts. He was the defensive MVP of the Gators win over the Oklahoma Sooners in the 2009 BCS National Championship Game, recording four tackles, and a shared sack during the game. He also was a second-team All-SEC selection.

As a junior in 2009, Dunlap played in 13 games. He missed one game, the SEC Championship, due to suspension after being arrested on driving under the influence of alcohol. During the season, he recorded 38 tackles and nine sacks and was a consensus first-team All-SEC selection. He ended his career with 84 tackles, 19.5 sacks, and three blocked kicks. After his junior year, Dunlap decided to forgo his senior season and enter the 2010 NFL Draft.

After his sophomore season, Dunlap was projected to be a first round and a possible top ten selection in 2010. His draft stock began to fall after a mediocre junior season and a DUI arrest. On January 11, 2010, it was announced that Dunlap would forgo his remaining eligibility and enter the 2010 NFL Draft. Dunlap attended the NFL Scouting Combine and performed all of the combine and positional drills. His overall combine performance was said to be underwhelming by multiple scouts and did not impress team representatives during the interview process.

On March 17, 2010, Dunlap attended Florida’s pro day and chose to perform multiple combine drills again. He improved his 40-yard dash (4.61s), 20-yard dash (2.68s), 10-yard dash (1.60s), bench press (22), and broad jump (9’4″). At the conclusion of the pre-draft process, Dunlap was projected to be a second round pick by NFL draft experts and scouts. He was ranked as the third best defensive end prospect by NFL analyst Mike Mayock, the fourth best defensive end by Scouts Inc., and was ranked the fifth best defensive end in the draft by DraftScout.com.

The Cincinnati Bengals selected Dunlap in the second round (54th overall) of the 2010 NFL Draft. Dunlap was the tenth defensive end drafted in 2010.

On July 28, 2010, the Cincinnati Bengals signed Dunlap to a four-year, $3.71 million contract that includes $1.77 million guaranteed and a signing bonus of $1.22 million.

Dunlap was inactive as a healthy scratch for the first two games of the regular season. On September 26, 2010, Dunlap made his professional regular season debut during the Bengals’ 20–7 victory at the Carolina Panthers in Week 3. Dunlap was inactive for another two games (Weeks 4–5), but made his return in Week 7 during a 39–32 loss at the Atlanta Falcons. During the game, he made his first career tackle on running back Jason Snelling to stop a four-yard gain in the fourth quarter. Dunlap was elevated on the depth chart after Antwan Odom was suspended and Johnathan Fanene and Frostee Rucker sustained injuries. Fanene, Odom, and Rucker were all placed on injured reserve where they would end the season. On November 14, 2010, Dunlap recorded two solo tackles and made his first career sack during a 23–17 loss at the Indianapolis Colts in Week 10. Dunlap made his first career sack on quarterback Peyton Manning for a four-yard loss in the second quarter. In Week 14, he collected a season-high four combined tackles and was credited with half a sack in the Bengals’ 23–7 loss at the Pittsburgh Steelers. On November 25, 2010, Dunlap made three solo tackles and had two sacks on quarterback Mark Sanchez during a 26–10 loss at the New York Jets in Week 12. His earned his first multi-sack performance of his career with his two sacks. Dunlap finished his rookie season in 2010 with 24 combined tackles (19 solo), 9.5 sacks, and three pass deflections in 12 games and zero starts. His 9.5 sacks led the team and set a franchise record for most sacks by a rookie.

During training camp, Dunlap competed to be a starting defensive end against Robert Geathers, Frostee Rucker, and Michael Johnson. Defensive coordinator Mike Zimmer named Dunlap the fourth defensive end on the depth chart to start the season, behind Robert Geathers, Michael Johnson, and Frostee Rucker. In Week 2, Dunlap collected a season-high four solo tackles during a 24–22 loss at the Denver Broncos. On October 2, 2011, Dunlap made his first career start in place of Robert Geathers. He finished the Bengals’ 23–20 victory against the Buffalo Bills with two combined tackles and a pass deflection. On November 6, 2011, he made three combined tackles, a pass deflection, and had a season-high two sacks on Titans’ quarterback Matt Hasselbeck in a 24–17 win at the Tennessee Titans. He was inactive for the Bengals’ Week 10 loss to the Pittsburgh Steelers due to a hamstring injury. Dunlap aggravated his hamstring injury and was inactive for three more games (Weeks 12–14). In Week 17, Dunlap collected a season-high six combined tackles and was credited with half a sack during a 24–16 loss to the Baltimore Ravens. He finished the season with 23 combined tackles (11 solo), 4.5 sacks, and three pass deflections in 12 games and one start.

The Cincinnati Bengals finished third in the AFC North with a 9–7 record and earned a wildcard berth. On January 7, 2012, Dunlap appeared in his first career playoff game and made one tackle during a 31–10 loss at the Houston Texans in the AFC Wildcard Game.

On July 15, 2013, the Cincinnati Bengals signed Dunlap to a five-year, $39.37 million contract extension with $11.70 million guaranteed and a signing bonus of $8 million.

Dunlap had a breakout season in 2015, recording a career best 13.5 sacks and earning his first Pro Bowl. He was ranked 70th on the NFL Top 100 Players of 2016.

In 2016, he started all 16 games, recording 49 tackles, eight sacks, three forced fumbles, and 15 passes defensed on his way to his second Pro Bowl. His 15 passes defensed was tied for eighth in the league and were the most by any non-defensive back.

In April 2016, Dunlap graduated from the University of Florida with a Bachelor of Science in Family, Youth and Community Services. In May 2016, Dunlap graduated from the University of Miami with a Master of Business Administration.

On August 28, 2018, Dunlap signed a three-year, $45 million contract extension with the Bengals through the 2021 season.

As the 2020 season progressed, Dunlap openly expressed his desire to want out of Cincinnati after losing playing time and questioning his usage by the coaching staff, including posting to his Twitter that he was selling his house in Cincinnati.

On October 28, 2020, Dunlap was traded to the Seattle Seahawks for center B. J. Finney and a 2021 seventh-round draft pick. Dunlap made his debut with the Seahawks in Week 9 against the Buffalo Bills. During the game, Dunlap recorded his first sack as a Seahawk on Josh Allen during the 44–34 loss.