The failure of Hungary's Olympic and 2014 world champion Krisztian Berki to qualify for the final raised hopes that Smith might finally land the gold as he had been the top performer in qualifying.
Smith produced a flawless display and sat on top of the standings with 16.033 until Whitlock, the final competitor on the horse, leapfrogged the Olympic silver medallist by just 0.1 of a point with a more dynamic programme that sparked jubilant celebrations among the hollering crowd at the Hydro Arena.
Travelling down and rotating around the block, Whitlock showed off his rigidly straight body lines and when he nailed his dismount, Smith was on his feet with the rest of the crowd.
The British duo stood shoulder-to-shoulder as they waited for Whitlock's score to come up and when the giant screen confirmed that it was the 22-year-old who was number one, Smith grabbed a Union Jack to begin the double celebration.
"It has been a tough year with glandular fever at the beginning of the year and this literally makes up for everything," a beaming Whitlock, who was hugged by Smith when he came off the competition area, told reporters.
"I am just absolutely over the moon. I am speechless. I can't believe it."
Smith, who won Britain's version of Dancing With the Stars during a two-year break from the sport after the London Olympics, was not surprised by the judges' verdict.
"The whole time I have been back I have been playing catch-up with Max," said Smith, who won a fourth world medal in the discipline after capturing a silver in 2010 and bronzes in 2007 and 2011.
"The whole idea was to prove that I am consistent, to prove that I can be an asset for the team. I am just so happy to be back."
Whitlock also scooped silver in the floor exercise to increase his championship tally to three, having helped Britain to finish second in the men's team final earlier in the week.
Before Saturday, the only Briton to have won world titles was Beth Tweddle, who won three between 2006 and 2010.
Whitlock (16.133) and Smith were the only finalists to break the 16-point barrier, leaving Japan's Kazuma Kaya and Armenia's Harutyun Merdinyan tied for bronze with a distant 15.500.
(Editing by Clare Fallon)
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