The Canadian club have progressed to the decider of the region's premier club competition by virtue of an away goals win over Costa Rica's Alajuelense.
The Impact defeated the Costa Ricans 2-0 in Montreal on March 18 before managing to score twice in the return bout in Alajuela to go through after a 4-4 aggregate.
Despite losing the second leg 4-2, Frank Klopas' side will now contest the CCL final against the winner of the other semi-final which pits Mexico's Club America against Costa Rica's Herediano with the latter holding a 3-0 lead.
Jack McInerney gave Montreal an unlikely lead in the 42nd minute after Alajuelense peppered the goals early when producing a neat low finish from Dominic Oduro's pinpoint cross from the right.
Pablo Gabas then responded for the home team with two goals in 14 minutes before the hour-mark but Andres Romero extended Montreal's overall lead to 4-2 when he outfoxed goalkeeper Dexter Lewis before firing home.
Alajuelense had to score three goals in less than 20 minutes in order to stage a remarkable comeback but late interventions from Allen Guevara and Jonathan McDonald was not enough to stop scenes of jubilation from the visiting Impact who are the first MLS to make the final since Real Salt Lake were beaten by Monterrey in the 2010/11 version.
2014/15 CONCACAF Champions League - semi-final second leg
Alajuelense (CRC): 4 (Pablo Gabas 46'/60', Allen Guevara 79', Jonathan McDonald 90+3') Montreal Impact (CAN): 2 (Jack McInerney 42', Andres Romero 72')
*Montreal wins on away goals after 4-4 aggregate
Estadio Alejandro Morera Soto, Alajuela, Costa Rica