Hardy attended Edmonds-Woodway High School in Edmonds, Washington, graduating in 2005. He then enrolled at Lewis–Clark State College, where he played for the school's college baseball team. Lewis–Clark won the National Association of Intercollegiate Athletics World Series championship in 2008.
The Kansas City Royals selected Hardy in the 22nd round of the 2008 MLB Draft. The Royals released Hardy during spring training in 2013.
Hardy signed with the Detroit Tigers in April 2013, and they assigned him to the Erie SeaWolves of the Class AA Eastern League. Hardy finished with a 2–2 record and a 1.63 earned run average (ERA) as a reliever before he was promoted to the Toledo Mud Hens of the Class AAA International League. He was pressed into duty as a starting pitcher due to a pitching shortage, but performed well. He finished the season with an 8–3 record and a 1.67 ERA between Double-A Erie and Triple-A Toledo.
Hardy was a non-roster invitee to spring training in 2014, and impressed as he competed for a role as the team's long reliever. The Tigers reassigned him to minor league camp towards the end of spring training. On June 15, 2014, the Detroit Tigers purchased Hardy's contract from Triple-A Toledo, and he was added to the 25-man roster. Hardy made his major league debut for the Detroit Tigers the next day in a game against the Kansas City Royals, pitching two scoreless innings, allowing one hit, walking two and striking out two. He performed well in his first major league season, posting a 2.54 ERA in 39 innings pitched.
Hardy made the Tiger roster for opening day in the 2015 season. On August 23, 2015, Hardy's homerless streak of 84 2⁄3 innings ended after allowing a home run to Mike Napoli. This was the longest active homerless innings streak in the major leagues. The last time Hardy had allowed a home run was to Jason Castro on June 27, 2014. Hardy holds the franchise record for the most appearances by a left-hander without allowing a home run, at 87, and was two appearances away from tying Bernie Boland's record for 89 homerless appearances. He would finish the season with a 3.08 ERA, while striking out 55 batters in 61 1⁄3 innings. He appeared in a team-high 70 games in 2015.
On May 12, 2016, Hardy was optioned to the Triple-A Toledo Mud Hens. He made seven appearances between June 6 and June 18 before being optioned to Toledo again. He was called up to the Tigers again in August, and pitched three scoreless innings of an August 9 game against the Seattle Mariners. For the 2016 season, Hardy made 21 relief appearances, posting a 1–0 record with a 3.51 ERA in 25 2⁄3 innings pitched.
Hardy throws a fastball in the 88–91 mph range that he will occasionally cut for late movement. His most effective pitch is an upper-70s curveball, which has yielded most of his strikeouts to date. He mixes in a changeup at 78–81 mph.