Hartman has collected 233 points (107-126=233), a plus-55 rating, 505 penalty minutes (PIM), 590 hits and 295 blocked shots in 506 career NHL contests during parts of 9 seasons with the Chicago Blackhawks, Nashville Predators, Philadelphia Flyers and Minnesota. He has also notched 15 points (6-9=15) in 35 career Stanley Cup Playoff matches. Hartman set career-highs in games played (82), goals (34), assists (31), points (65), PIM (95), power-play goals (7) shots (239) and plus-minus (plus-31) during the 2021-22 season with Minnesota.

Chicago selected Hartman in the first round (30th overall) of the 2013 NHL Draft, and he made his NHL debut on February 13, 2015 against New Jersey. He is the first player in NHL history to be born in South Carolina. Minnesota originally signed Hartman to a two-year contract on July 1, 2019.