The 20-year-old striker lit up an exciting semi-final with a virtuoso performance which put Killie into their first major final since 2001.
Jim Jefferies' side will meet the winners of the other semi-final, between St Johnstone and Hibernian, in the Hampden final on March 18, but if their talismanic Scotland B international can replicate this terrific form the Rugby Park side will have nothing to fear.
Naismith gave his side the interval lead when he confidently drilled home a Colin Nish flick-on from 16 yards out with 29 minutes gone.
He then scored a wonderful goal in the 71st minute to double their lead before a penalty six minutes later, after he had been fouled by Bairns defender Kenny Milne inside the penalty area, completed a great night for the youngster and the Killie fans.
The pre-match build-up evoked all the feelings of a traditional cup semi-final and the 15-minute delay to kick-off to allow fans to get inside the stadium only added to the sense of excitement.
New Scotland manager Alex McLeish, sitting in the stand, witnessed some snappy shadow boxing from both sides before the first effort on goal arrived after five minutes.
Russell Latapy's looping free-kick to the back post was met by the unmarked Jack Ross 10 yards out but Killie keeper Alan Combe saved the defender's powerful header with confidence.
As Falkirk began to edge possession, midfielder Vitor Lima drilled in a 25-yard shot which went inches past the post, seconds before Killie striker Naismith tested Kasper Schmeichel with a right-footed drive which the Bairns keeper grabbed with assurance.
Unencumbered by the threat of losing SPL points, both sides went toe-to-toe for the chance of Hampden glory and despite a frustratingly strong wind, a compelling, if less than enthralling battle continued.
When the breakthrough came in the 29th minute for Kilmarnock, it owed little to weeks of training-ground preparation.
A Frazer Wright punt from wide on the left was flicked on by the lanky Nish under pressure from Bairns defender Darren Barr, and Naismith stole in behind the Falkirk defence to rifle past Schmeichel from around 16 yards out.
The goal raised the tempo in the stands a notch, as did a couple of strange refereeing decisions by Kenny Clark as the first 45 minutes drew to a close.
Falkirk became almost reckless as they went in search of the equaliser, at times leaving just one defender to cope with the pace of Naismith.
However, it was clear by the time the whistle sounded that Jim Jefferies' side needed a pep-talk to discuss how they were going to handle their lead.
But whatever the Killie boss said to his players presumably did not include asking them to calm the game down, because after the interval the Ayrshire side resumed their free-for-all with Falkirk.
Amid increasing niggly fouls by either side, the ball was battered from end to end, rarely spending more than the occasional fleeting moment on the ground.
In the 57th minute, however, the Bairns should have equalised when Carl Finnigan was left with only Combe to beat from 15 yards out.
But the Falkirk striker swung wildly at the ball and the Killie keeper blocked with his legs.
Seconds later at the other end, Nish set up Naismith again and the Scotland Under-21 star had a great opportunity to seal a place in the final, but his right-footed drive was brilliantly blocked by Schmeichel.
But in the 71st minute Killie put one foot in the final when Naismith beat the Falkirk offside trap to latch onto a Simon Ford pass.
Naismith's first touch to control the ball was only bettered by his second, which saw him drive an unstoppable shot from the edge of the box past Schmeichel.
The Killie striker was far from finished with his night's work.
In the 77th minute Naismith was fouled in the box by Milne as he wriggled towards goal, allowing him to hammer home his hat-trick from the penalty spot.
Never had the sponsor's man-of-the-match award been so easy to pick.