MCA's Yaqoob Ali claimed a five wicket haul as the Knights were dismissed for 202 chasing an unlikely 355 for victory.
Ali's dismissal of Shane Getkate (20) sparked a collapse that saw six wickets fall for just 29 runs - the Knights faltering from a respectable 106 for 3 to 135 for 9.
Ballymena's Robert McKinley gave the innings a veneer of respectability as he added 67 in a last wicket partnership with Jacob Mulder (5*) - the highest stand of the game for the Knights.
McKinley top scored with 56 from just 43 balls (9 fours, 1 six), before becoming the last of Ali's five victims.
Opener Chris Dougherty battled bravely for his 44 which included seven boundaries, but found little in the way of support as the Knights' batting frailties were once again exposed by the ruthless Lightning attack.
Max Sorensen (2-53) removed James Cameron-Dow (3) early, whilst John Mooney claimed the pivotal wicket of his Knights counterpart - James Shannon having his off-stump removed.
It was then the turn of Lightning's spinners to bring the game to a conclusion as Ali (5-51) and international George Dockrell (2-35) combined to bowl Lightning to the win, despite McKinley's late pyrotechnics.
Lightning then claim their 7th trophy in the three seasons of Inter-Provincial competition, affirming their undoubted dominance at this level. .
HANLEY ENERGY INTER-PROVINCIAL CHAMPIONSHIP
At Rathmines, Day 3 close of play
LEINSTER LIGHTNING 337/9 dec and 191/1 dec (30 overs, F McAllister 105*, J Tector 57)
NORTHERN KNIGHTS 174 all out and 202 all out (51.5 overs, R McKinley 56, C Dougherty 44, J McCollum 21, S Getkate 20, Y Ali 5-51, G Dockrell 2-35, M Sorensen 2-53)
Leinster Lightning beat Northern Knights by 152 runs