The victory gave the visitors a triumphant 3-0 lead in the five-match series.
Misbah's innings, spiced with four fours and two sixes off 109 balls, revived a stuttering chase and guided Pakistan past the host's modest 171 all out at 177-7 with 29 balls to spare.
Misbah's partnerships with Umar Akmal (30) and Hammad Azam (36) rescued Pakistan after it slumped to 12-3 and then 49-4.
Fast bowler Ravi Rampaul ripped through the Pakistan top order with 4-32 while legspinner Devendra Bishoo later claimed 3-42 to keep West Indies in the hunt.
But Misbah and Wahab Riaz, who scored 17 not out, steered a wobbly Pakistan home with an unbroken eighth-wicket stand of 29.
Earlier, after a rain-delayed start reduced the contest to 45 overs per side, West Indies had an encouraging start through a second-wicket stand of 86 between Lendl Simmons and Darren Bravo.
Simmons struck four fours and two sixes in 51 off 64 balls while left-hander Darren Bravo hit three fours and a six in 47 off 77 deliveries.
But once they were dismissed, the last seven West Indian wickets tumbled for 40 runs.
Offspinner Saeed Ajmal ended with 3-29 while left-arm seamer Wahab Riaz blew through the middle order with 3-38.
Mohammad Hafeez, who took 2-31, made the early breakthrough with the wicket of Devon Smith for the third time in the series.
But Simmons and Bravo fought back brilliantly in a fluent partnership that lit up an overcast Kensington Oval.
Simmons eventually chipped a return catch to Ajmal at 92-2.
Hafeez returned to make another crucial breakthrough when Bravo was leg before wicket at 118-3.
The other batsmen failed to fire with Marlon Samuels and Kirk Edwards struggling to get the ball away despite each scoring 18.
Pakistan's chase was derailed by Rampaul's aggression as he struck with his first two deliveries to remove Ahmed Shehzad and Asad Shafiq.
Shehzad, a century-maker in the last match, top-edged a hook while Shafiq edged low to second slip.
Rampaul made it 12-3 when Hafeez also miscued a pull and West Indies was rampant.
Umar Akmal dominated a fourth-wicket stand of 37 with Misbah before Rampaul produced a fiery bouncer that clipped Akmal's glove on the way through to the wicketkeeper at 49-4.
But Misbah found another able ally in Hammad Azam and the pair added 78 off 119 balls to push their side to the brink.
Bishoo claimed three wickets to even the balance as Azam, captain Shahid Afridi and Mohammad Salman departed in quick succession.
But Misbah stood firm with Wahab to ensure the series victory.
The fourth match in the series is at the same venue on Monday.