Guptill carried his bat and finished the innings unbeaten on 237 from 163 balls as New Zealand posted an imposing 393 for six from their 50 overs.
The knock was forged on steady beginnings and his back-foot play from the spinners was a feature as he used the late cut nicely.
"It's a pretty cool feeling, to be fair," an elated Guptill said after he walked off the field to a rousing ovation.
Before the World Cup, there were concerns around his form as he bumbled his way through the seven-match lead-up series against Sri Lanka. The 28-year-old passed 50 only once against a poor Sri Lankan bowling attack and three ducks were worrying.
It followed on from a middling 2014, when he averaged 30 but his strike rate dipped below 70 as he struggled to push singles and the dot balls mounted.
But those worries have passed.
When he brought up his double century -- becoming the first New Zealander to do so -- he pointed his bat to towards the team dugout, removed his helmet and let out a roar.
The Aucklander was dropped at square leg in the first over by Marlon Samuels when he had four runs next to his name -- cricket can be an unforgiving sport.
"Obviously there's pressure but you've just got to try and put it behind you and just watch the ball as hard as you can and play it accordingly," Guptill said. "And, that's what I tried to do today, and luckily it paid off."
The boisterous Wellington fans chanted his name as his innings progressed and he vindicated their decision to attend the game with a show-stopping performance -- the second-highest one-day score of all.
"I just want to thank the crowd for coming out and supporting us," Guptill said.
The West Indies bowlers dropped their heads as they couldn't find anything that resembled a good length and Guptill had a bat as his weapon and an eye that couldn't miss a trick.
His innings spanned 225 minutes, included 24 fours and 11 sixes. It was the seventh century of his ODI career. But the most significant by some margin.
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