Gardenhire finishes 132-241 in two-plus seasons as Tigers skipper. He signed a three-year deal when he was hired before the 2018 campaign.
"This afternoon, when I got here to the office, I went to Gardy's office to talk baseball stuff," Tigers general manager Al Avila said, according to Evan Petzold of the Detroit Free Press. "At that point, we started talking, and he mentioned to me he was going to retire. He wasn't feeling well from a health perspective."
Gardenhire's .354 winning percentage makes him the least successful manager in Tigers history. With a shortened season, the club had the potential to make the postseason this year but ultimately was eliminated from contention.