A 31-year-old right-hander, Chacin was 15-8 with a 3.50 ERA in 35 starts last season. He also started openers for Colorado in 2013 and San Diego in 2017.
"Jhoulys earned the honor from what he did last year and he deserves it for sure," Brewers manager Craig Counsell said Thursday.
Chacin allowed one run and one hit over 5 2/3 innings in the NL Central tiebreaker game against the Chicago Cubs and pitched five shutout innings in a Division Series start against Colorado. He went 1-1 with a 2.45 ERA in two starts against the Los Angeles Dodgers in the National League Championship Series.