The Reds had a 2-0 victory over north Belfast rivals Crusaders, who were beaten finalists in the last two seasons, to keep alive hopes of a three-trophy haul this season.
With January's League Cup win behind them, and a 14 point advantage over Crusaders at the top of the Danske Bank Premiership with only five games to go, Tommy Breslin's Cliftonville will go into the decider in full belief they can win the Irish Cup for the first time in 34 years.
It took the Reds until the 67th minute at The Oval to find the breakthrough on Saturday evening.
George McMullan scored from a penalty which was quickly followed up a minute later by Joe Gormley's goal that all but ended Crusaders' challenge.
Cliftonville are now looking for their ninth Irish Cup honour - their last a 3-2 win over Portadown in 1979.
Glentoran were first to book their place in the final. The 20-time winners beat Portadown 1-0 in the early kick-off at Windsor Park.
Marcus Kane's goal in the 79th minute proved enough to separate the sides, as the substitute rose highest to head home a Richard Clarke corner.
The last-four result sends Eddie Patterson's side into their first decider since 2006, and guarantees a Europa League spot for next season.
The Irish Cup Final between Cliftonville and Glentoran will take place on Saturday 4 May at Windsor Park in Belfast.
Irish Cup semi-final results:
Crusaders 0-2 Cliftonville
Cliftonville: McMullan pen 67, Gormley 68
Portadown 0-1 Glentoran
Glentoran: Kane 79