Williams was named the starting nose guard prior to Alabama's 2018 season opener against Louisville.

[11] On January 11, 2019, Williams announced that he would forgo his remaining two years of eligibility and enter the 2019 NFL draft.

On August 26, 2019, Williams was fined $21,056 for a late hit on Matt Schaub in the second preseason game against the Atlanta Falcons.

In Week 9 against the Miami Dolphins, Williams recorded his first career sack on Ryan Fitzpatrick in the 26–18 loss.

[18] In Week 10 against the New York Giants, Williams recorded his first career fumble recovery, securing a football lost by Golden Tate on the final play of the game in the Jets' 34–27 victory.

Overall, Williams would finish his rookie season with 28 tackles, 2.5 sacks and 1 fumble recovery in his 13 games played.

In Week 12 against the Dolphins, Williams recorded 1.5 sacks on Ryan Fitzpatrick and forced a fumble on running back Matt Breida that was recovered by the Jets during the 20–3 loss.

[24] On October 4 in a game against the Tennessee Titans, Quinnen and his brother Quincy, who joined the Jets earlier that season, made NFL history by each recording a sack in the win.