Seattle Mariners centre fielder Kyle Lewis won the AL Rookie of the Year award unanimously.
Williams made history Monday becoming the first pitcher to win Rookie of the Year without recording a save or making a start during his award-winning season -- reflecting the increased importance of the bullpen in today's game. He is the first Rookie of the Year for Milwaukee since Ryan Braun in 2007.
"I don't really think that saves are the end-all be-all," Williams said on a conference call during a vacation in Jamaica. "If I come up in the seventh inning and I go through one through five, I think that that can be pretty valuable as well."
San Diego Padres second baseman Jake Cronenworth and Philadelphia Phillies infielder Alec Bohm tied for second in NL balloting by the Baseball Writers' Association of America.
Williams, a St. Louis native, was selected by Milwaukee in the second round of the 2013 draft. He had Tommy John surgery while he was in the minors and made his big league debut last year.
This season, Williams teamed with closer Josh Hader to form a shutdown tandem at the back end of the Brewers' bullpen. He allowed one earned run in 22 appearances _ a home run by Pittsburgh's Colin Moran on July 27.
Featuring a devastating changeup and a four-seam fastball that gets into the upper 90s, Williams was practically unhittable. The 26-year-old right-hander went 4-1 with a microscopic 0.33 ERA, striking out 53 in just 27 innings.
The last reliever to take home the honour in either league was Craig Kimbrel for Atlanta in 2011.
Williams missed Milwaukee's loss to the champion Dodgers in the first round of the playoffs because of shoulder soreness.
"I'm doing a little bit of rehab still, but it's feeling good," Williams said.
The Managers of the Year will be announced by the BBWAA on Tuesday night, followed by the Cy Young Awards on Wednesday and the MVPs on Thursday.