The fourth seed Bruins closed out the series 4-1 against the sixth seeded Rangers to set up the showdown with the top-seeded Penguins for a place in the Stanley Cup Finals.
It is their first trip back to the Eastern Finals since the 2010-11 season where they went on to win the Stanley Cup.
Boston fell behind after Dan Girardi scored a power-play goal in the opening period but 22-year-old Torey Krug continued his strong post-season with a power-play goal of his own after three minutes of the second period.
It was Krug's fourth goal in his first five play-off games and sparked the Bruins into action.
Gregory Campbell snapped the tie with a goal 10 minutes later and he added a second goal in the dying seconds of the game when he managed to backhand the puck into an empty net despite being hooked right before the attempt.
"It was a tough series. They played hard and they are really similar to us," Campbell said.
"It was a physical series and most games could have gone either way but we fought hard."
Bruins goaltender Tuukka Rask saved 28 of 29 shots.
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- Torey Krug