The Cubs, who also agreed to a one-year deal with right-hander Kohl Stewart this week, are looking to bolster a pitching staff after it traded Yu Darvish to San Diego in December and lost Jon Lester, Tyler Chatwood and Jose Quintana in free agency this offseason.
Williams, 28, struggled in the pandemic-shortened 2020 season, going 2-8 with a 6.18 ERA while giving up the most home runs (15) in the majors. He fared little better in an injury-plagued 2019 campaign, where he went 7-9 with a 5.38 ERA in 26 starts.
The Cubs hope Williams will be able to recapture the form he showed in 2018. The right-hander finished 14-10 with a 3.11 ERA but had a sterling 1.38 ERA after the All-Star break.
Williams, who spent the entirety of his five years in the majors with Pittsburgh, is 31-37 with a 4.43 ERA for his career.