During the pre-draft process, Richardson cited the Kansas City Chiefs, Miami Dolphins, Oakland Raiders, Jacksonville Jaguars, and Seattle Seahawks as the teams who expressed the most interest.

The Jets used Richardson as a fullback in six plays during the 2013 season in games against the Atlanta Falcons, the Buffalo Bills, the Carolina Panthers, and the Miami Dolphins.

In a week 15 game against the Panthers, Richardson became the first NFL defensive lineman to score a rushing touchdown since B. J. Raji did so for the Green Bay Packers in 2011.

[10] Richardson played 16 games (started 15) in 2013 making 78 tackles, a pass defended, a forced fumble, 3.5 sacks, and 2 rushing touchdowns.

On February 2, 2014, it was announced that Richardson had won the 2013 NFL Defensive Rookie of the Year award, edging out Buffalo Bills linebacker Kiko Alonso by a margin of 23 votes to 19.

[13] During the 2014 year, Richardson started all 16 games making 66 tackles, 8 sacks, 1 pass defended, 1 forced fumble, and 1 safety enforced.

On July 2, 2015, Richardson was suspended for the first four games of the 2015 regular season due to failing the league's substance abuse policy related to marijuana.

[16] On October 15, 2015, Richardson played in his first game of the season and recorded three combined tackles, and was credited with half a sack on Washington Redskins' quarterback Kirk Cousins in a 34–20 victory.

On April 18, 2016, the Jets picked up Richardson's fifth-year option on his rookie contract that was worth $8.06 million for 2017 and fully guaranteed.

[18] After serving his one-game suspension during the New York Jets' season-opener, he made his season debut the following week against the Buffalo Bills and recorded four solo tackles during the 37–31 victory.

On September 25, 2016, Richardson recorded five combined tackles and was credited with half a sack on Alex Smith, as the Jets were defeated by the Kansas City Chiefs 3-24.

The following game, he earned six combined tackles and made his only solo sack of the season on Baltimore Raven' quarterback Joe Flacco in a 24–16 victory.

[21] Before the beginning of the 2017 season, the New York Jets fielded offers from the Dallas Cowboys, Denver Broncos, and Seattle Seahawks.

On October 8, 2017, Richardson intercepted a pass attempt from Los Angeles Rams' quarterback Jared Goff and also returned a fumble recovery for 20-yards during a 16–10 victory.

During Week 14 against the Jacksonville Jaguars, Richardson was ejected for the first time in his NFL career after being involved in a brawl that occurred during the closing seconds of the fourth quarter.

[25] On the season he had 15 starts in 15 games and finished with a total of 44 combined tackles (27 solo), 1 sack, 1 pass defended, 1 interception, and a forced fumble.