[5] On January 6, 2015, Williams announced via Twitter that he decided to forgo his senior season and declare himself eligible for the 2015 NFL draft.

[8] On March 31, 2015, Williams attended Florida State's pro day and chose to stand on the majority of numbers from the combine.

Over 150 scouts, team representatives, and media members attended Florida State's pro day, including head coaches Sean Payton (New Orleans Saints), Lovie Smith (Tampa Bay Buccaneers), Mike Tomlin (Pittsburgh Steelers), Todd Bowles (New York Jets), and Ken Whisenhunt (Tennessee Titans).

[9] During the draft process, Williams had private workouts and meetings with a few teams, including Buccaneers, Detroit Lions, Baltimore Ravens, and Dallas Cowboys.

At the conclusion of the pre-draft process, NFL draft experts and scouts projected Williams to be a late first or second round pick.

The pick used to select Williams originally was acquired from the Miami Dolphins along with Dannell Ellerbe in exchange for Kenny Stills.

[20] Throughout training camp, Williams competed against Kyle Wilson, Damian Swann, Stanley Jean-Baptiste, and Delvin Breaux for the starting nickelback on the depth chart.

[24] He made his professional regular season debut and first career start in the Saints' season-opener against the Oakland Raiders and recorded five combined tackles and a pass deflection in their 35–34 loss.

On September 21, 2016, Williams suffered a serious concussion while attempting to make a tackle on New York Giants tight end Larry Donnell.

[29] Williams entered training camp competing for a job as the starting cornerback, opposite Breaux, against rookie first round pick Marshon Lattimore.

Payton named him one of the starting cornerbacks with Ken Crawley to begin the regular season after Breaux suffered a fractured fibula during camp.

The following week, he recorded a season-high ten combined tackles and a pass deflection in the Saints' 36–20 loss to the New England Patriots.

Although he played well, Williams was demoted to a reserve role behind Marshon Lattimore and Ken Crawley due to an unspecified disciplinary issue prior to their Week 4 matchup at the Miami Dolphins.

On November 26, 2017, he made three solo tackles, three pass deflections, and intercepted Jared Goff in the Saints' 26–20 loss at the Los Angeles Rams.

[37] In Week 2 against the Las Vegas Raiders on Monday Night Football, Williams recovered a fumble lost by running back Jalen Richard during the 34–24 loss.

[40][41] In a game against the Buccaneers on October 31, 2021, Williams intercepted Tom Brady's pass intended for Chris Godwin and returned it 40 yards for a game-clinching pick six, and his second career defensive touchdown.

The Tallahassee Police Department initially identified the accident as a hit and run, but downgraded the incident, issuing Williams two tickets one for driving on a suspended license.