In Bell's senior year he led Ridgeland to the Georgia class AAAA state championship game but lost to Sandy Creek 41–10.

[3][4] Bell played in all 13 games as a backup his freshman season in 2013, but made his first career start on January 3, 2014, in the Discover Orange Bowl where he recorded his first collegiate interception.

[10] He also attended private workouts and visits with multiple teams, including the Minnesota Vikings, Buffalo Bills, Atlanta Falcons, Los Angeles Rams, Tampa Bay Buccaneers, Jacksonville Jaguars, Pittsburgh Steelers, and Tennessee Titans among others.

Head coach Sean Payton named Bell a backup safety to start the regular season, behind starters Jairus Byrd and Kenny Vaccaro.

[23][24] On September 9, 2016, Bell made his professional regular season debut in the New Orleans Saints' home-opening 35–34 loss against the Oakland Raiders.

[25] He finished his rookie season in 2016 with a total of 87 combined tackles (61 solo), four pass deflections, two forced fumbles, and a sack in 16 games and 14 starts.

[29] During training camp, Bell competed against rookie second-round pick Marcus Williams for the job as the starting free safety after it was available following the departure of Jairus Byrd.

[31] The following week, Bell made 11 combined tackles (nine solo) and sacked Jared Goff once during a 26–20 loss at the Los Angeles Rams.

[31] The following week, he made eight combined tackles (five solo) during a 29–24 loss at the Minnesota Vikings in the National Football Conference (NFC) Divisional Round.

He finished his third season with a career-high 89 combined tackles (63 solo), three pass deflections, one sack, and one forced fumble in 16 games and eight starts.

Defensive coordinator Dennis Allen chose Bell as the starting strong safety over rookie C. J. Gardner-Johnson to begin the season and paired him with Marcus Williams.

On September 22, 2019, Bell recorded nine combined tackles (five solo) and recovered a fumble that teammate Eli Apple caused from running back Chris Carson and returned it 33–yards and to score his first career touchdown as the Saints defeated the Seattle Seahawks 33–27.

[36] During Week 7, Bell recorded a team high eight combined tackles (seven solo) and forced a fumble on wide receiver Anthony Miller and recovered it in the 36–25 victory at the Chicago Bears.

In Week 14, Bell recorded a team high 13 combined tackles (nine solo) and sacked Jimmy Garoppolo during a narrow 48–46 loss against the San Francisco 49ers.

Head coach Zac Taylor named him the starter to begin the season, alongside free safety Jessie Bates.

Defensive coordinator Lou Anarumo retained Bell and Jessie Bates as the starting safeties to begin the 2021 NFL season.

He was inactive as a healthy scratch during a Week 18 loss to the Cleveland Browns as head coach Zac Taylor opted to rest his starters.

On January 22, 2022, Bell made six combined tackles (five solo) and one sack as the Bengals won 19–16 at the Tennessee Titans in the AFC Divisional Round.

On January 30, 2022, Bell started in the AFC Championship Game at the 2021 Kansas City Chiefs and made six combined tackles (three solo), one pass deflection, and intercepted a pass thrown by Patrick Mahomes to wide receiver Tyreek Hill in overtime as the Bengals won 27–24 and advanced to the Super Bowl LVI.

[43] On February 13, 2022, Bell started in Super Bowl LVI and made seven combined tackles (five solo) as the Cincinnati Bengals lost 20–23 against the Los Angeles Rams.