A goal behind with just 76 seconds left, Chicago scored twice in 17 seconds to win 3-2, taking the best-of-seven series 4-2 after three wins in a row.
It was the Blackhawks fifth NHL Championship title and ended a season that began with the team setting a record by earning at least one point in their first 24 games.
Coach Joel Quenneville said: “It was one of those seasons. We were saying we’re almost charmed, the way we started the season and the way we ended.
“Nobody saw that one coming either way. But it was one of those seasons, fairytale ending and an amazing season.”
It was a nightmare end for Boston, whose fans had believed the series was headed back to Chicago for a winner-takes-all showdown when Milan Lucic put the Bruins 2-1 ahead with about eight minutes to play. But, with Blackhawks netminder Corey Crawford taken off in favour of an extra attacker, Bryan Bickell tied the game with a tap in from the side of net moments before Dave Bolland sealed the Cup for Chicago.