 In the playoffs, his team defeated their rivals, the Toronto Maple Leafs, 4–3 and advanced to the second round against Tampa Bay Lightning, losing in five games.In the 2018–19 season, Cassidy led the Bruins to an appearance in the 2019 Stanley Cup Finals, where the team lost to the St. Louis Blues in seven games.On September 11, 2019, he signed a multi-year contract extension.