Per club and Major League Soccer policy, terms of the agreement will not be disclosed.
The American goalkeeper becomes the third player to sign with the Impact for its inaugural season in MLS, and the second player from the 2011 edition.
"I'm very excited and proud to get back in Montreal," said Evan Bush. "I'm pleased to be a part of the plans as the club moves to Major League Soccer. This past season opened my eyes on how professional this organization is. I am ready to take on the next challenge."
"Evan has shown in 2011 that he can be a top goalkeeper," said Impact head coach Jesse Marsch. "With his performances during the last season, he has earned the right to join the Impact for its move to MLS. I am looking forward to challenging him at the next level."