One of track and field's rising stars, McMaster eased to victory in 48.25 seconds, well ahead of Jeffery Gibson of the Bahamas (49.10) and Jamaica's Jaheel Hyde (49.16).
"I can guarantee they are jumping for joy," McMaster, 21, said of the residents back home. "Everyone gathered into a big spot to watch this on TV and I can imagine how they are right now.
"For me it is a big deal, what we have been though. This is the first positive of a great future for the British Virgin Islands."
The scenes of celebration are markedly different from what transpired last September, when Hurricane Irma -- the most powerful storm ever recorded in the Atlantic Ocean -- ripped through the country.
There was little immediate respite, as Hurricane Maria then slammed the British Virgin Islands two weeks later.
The path of destruction left 134 dead, including McMaster's mentor and coach, Xavier "Dag" Samuels.
Eighty percent of buildings were either damaged or destroyed, power was out and 6,000 people -- one fifth of the entire population -- were left homeless. Tourism -- so pivotal to the country's economy -- took a major hit. Three billion dollars was needed to rebuild the island and much of the work is still being done.
One of Samuels' key words was "guidance" and McMaster has that tattooed on his arm.
"Tonight the gold meant a lot to the country, but I did what my coach would have wanted me to, go out there and run my race," said McMaster.
"He's with me everywhere I go with the band and the tattoo on my arm. So today I came out here and had fun like he always would also tell me before my race. Enjoy the moment, don't pressure yourself in the race."
McMaster recorded the fastest time of 2017 at 47.80 seconds but failed to win a medal at the world championships in London because he was disqualified for a false start.