On November 9, 2020, Williams was named the NL Rookie of the Year, becoming the first relief pitcher to win the award since Craig Kimbrel in 2011.

After allowing only a single earned run in 14 relief appearances during August, he was named NL Reliever of the Month for the second time.

[13] On September 29, 2021, it was announced that Williams would miss the remainder of the season after fracturing his pitching hand after drinking alcohol and punching a wall following the celebrations following the team's NL Central Division title clinch the Sunday before.

[16][17] On January 13, 2023, Williams agreed to a one-year, $3.35 million contract with the Brewers, avoiding salary arbitration.

In the 2024 National League Wild Card Series against the New York Mets, Williams was brought in to close Game 3 with the Brewers leading 2–0.

He allowed four runs in the top of the ninth inning, as Milwaukee eventually lost the game and their sixth straight playoff series.

[24] On December 13, 2024, the Brewers traded Williams to the New York Yankees in exchange for Nestor Cortés Jr., Caleb Durbin, and cash considerations.

[25][26] Williams has two primary pitches: a four-seam fastball and a circle changeup with screwball-like movement while rotating the ball off the ring finger during release, which is also similar to a cricket leg-spinner bowling a googly,[citation needed] but at a much faster pace of around 85 mph and with a very high spin-rate of 2,852 rpm.