Chasing a target of 244 runs to win, West Indies failed to counter New Zealand's bowling attack and were eventually bundled out for 124 runs in 16.3 overs with Shai Hope absent hurt.
Tim Southee was the pick of the bowlers for the Black Caps for his figures of three for 21 while Trent Boult and Ish Sodhi added two wickets each to their name.
Meanwhile, Anaru Kitchen also chipped in with a wicket.
For the Caribbean side, third drop Andre Fletcher was the highest contributor with his 46-run knock.
Earlier, the Kane Williamson-led side had won the toss and elected to bat first.
Opener Martin Guptill and Munro provided New Zealand with a perfect start, sharing a huge 136-run stand for the first wicket.
While Guptill notched up a 63-run knock off 38 balls, Munro smashed a 53-ball 104 runs including three boundaries and 10 sixes to help the home side post a score of 243-5.
En route to the century, Munro also became the first cricketer to hit three hundreds in T20 internationals.
With this, the 30-year-old moved ahead of four players, including West Indies' Chris Gayle, on two T20I centuries.
The Bay Oval marked the second century of the recently-turned opener. Earlier, he had scored 101 against Bangladesh in January last year.
Munro's highest score is an unbeaten knock of 109 in the series against India in November.
With the win, the Black Caps, who have never beaten a side by more runs in this format, have climbed up in rankings to become number one T20 international team in the world.
It should be noted that the second game between the two sides was washed out on Monday while the opening T20I was won by New Zealand by 47 runs in Nelson. (ANI)