On July 1, 2017, Kunitz left the Penguins as a free agent and signed a one-year, $2 million, contract with the Tampa Bay Lightning. The Lightning announced through its social media account that Kunitz would wear the #14. Kunitz had previously worn the number with the Penguins and the Ducks. Kunitz recorded 13 goals and 29 points during the season, but just one assist in the playoffs as the Lightning lost in the Eastern Conference Final to the eventual champion Washington Capitals in 7 games.