The Londoner, 25, pipped fast-finishing Jamaican Lansford Spence to take first place, with Welshman Christian Malcolm earning bronze.
He also thoroughly upstaged his more illustrious team-mate Marlon Devonish, who trailed home in fifth.
Baptiste had earlier set a new personal best in his semi-final and maintained his superb form to finish the final in 20.45 seconds – 0.04 quicker than Spence.
A European junior champion at the 100m as an 18-year-old, Baptiste is now setting his sights on challenging the world’s elite.
He said: “Obviously next for me is the tough job of trying to compete with Usain Bolt and the rest of the big guys, but I’m looking forward to it.”
Bolt is not in Delhi due to injury.
Elsewhere, Dai Greene won 400m hurdles gold for Wales, with compatriot Rhys Williams taking bronze, while Scotland’s Eilidh Child won silver in the women’s 400m hurdles.
Away from the track, English cyclist Lizzie Armitstead earned silver in the women’s road race, in which Olympic champion Nicole Cooke of Wales was fifth. Scotland’s David Millar won bronze in the men’s road race as England’s Mark Cavendish finished a disappointing seventh.
Shooter Aaron Heading bagged gold for England in the men’s trap singles, while English archer Alison Williamson took silver after being beaten into second place by 16-year-old Indian starlet Deepika Kumar in the individual recurve.