Zastryzny began the 2016 season with Tennessee, and received a mid-season promotion to the Iowa Cubs of the Class AAA Pacific Coast League. On August 19, the Cubs promoted him to the major leagues. Zastryzny made 11 appearances for the Cubs to finish 2016, and finished 1-0 with a 1.13 ERA. The Cubs would eventually win the 2016 World Series, ending their 108-year drought. Zastryzny won his first World Series title. Zastryzny was added to the roster for the 2016 National League Championship Series, replacing Tommy La Stella who had been on the roster for the 2016 National League Division Series. Although eligible to play, he did not appear in any NLCS games. Zastryzny was replaced by Kyle Schwarber on the roster for the 2016 World Series. He was designated for assignment on September 1, 2018. He was outrighted to AAA on September 3, 2018. Zastryzny was released by the Cubs organization on March 25, 2019.