The race was re-run on Sunday following complaints that Williamson had jumped the gun when he finished first on the previous day.
Electronic equipment failed to alert runners to the false start, so judges ordered the race to be held again 24 hours later.
Williamson proved that he was the rightful owner of the gold medal by leading from the gun to clock a time of 10.22 seconds – faster than his earlier ‘win’.
The finishing positions were the same as in the original final with Zhang Peimeng of China in second and Canada's Neville Wright in third.
Williamson, 21, held his finger to his lips as he crossed the line to silence doubters who thought he could not repeat his performance.
“I had to stay calm when I heard the first result was cancelled,” he said afterwards. “I slept well last night and was sure I could do it again.”
Williamson, a sports science student at Middlesex University who has Olympic ambitions next year, joked: “If they want me win this race for a third time, I'm happy to.
“We were told at one stage that he was disqualified after the first final, which would have been grossly unfair,” British team manager Yvette Luker said.
“He is often very fast out of the blocks and he has shown here that he has a big future.”
The showpiece race was just one highlight on a day when 43 gold medals were won at the University Games, which are being held in Bangkok.
Also on the track, Samir Khadar of Algeria won the men's 1,500-metres in an incredibly close race when he finished in 3:39.62 beating Spaniard Alvaro Rodriguez by only 0.16 seconds.
Russia's Olesya Chumakova won the women's race over the same distance in another close finish, with Ukrainian Tetyana Holovchenko just a second behind.
In the pool Germany's Helge Meeuw confirmed he is one of the best student swimmers in the world by adding the 100-metre title to his 50-metre backstroke title.
Yana Klochkova's appearance at the games has shown that the event draws top-class talent. The world record holder and reigning double Olympic champion from Ukraine put on an awesome display to win the women's 400-metre individual medley.
Federica Pellegrini of Italy – another Olympic medalist – won the 200-metre freestyle in a games' record time to go with her 400-metre freestyle gold.
The US team took the men's 4x200-metre freestyle relay, adding to their 4x100-metre title.
Russia remained at the head of the overall medals table after being on target again in the shooting, picking up four golds on Sunday.
Ukraine mounted a charge up the table by harvesting four artistic gymnastics golds, plus one in the fencing and another with Klochkova's swimming success.
At the end of Sunday – the fourth of ten days of competition – Russia had 16 golds, China 13 and Ukraine nine.
Japan, South Korea, Germany and the United States were close behind on eight golds each.
Monday's action sees 38 golds up for grabs, including in the first day of the judo tournament.—Agencies
Medal standings
Medal standings on Sunday of countries who have won at least one gold medal at the World University Games.
(Tabulate under gold, silver, bronze, total):
Russia 16 10 17 43
China 13 16 11 40
Ukraine 9 12 10 31
Japan 8 9 4 21
South Korea 8 5 8 21
Germany 8 4 4 16
United States 6 6 7 19
Italy 5 3 5 13
Thailand 3 5 2 10
Taiwan 3 2 4 9
Kazakhstan 3 2 3 8
Canada 3 1 3 7
Iran 3 1 2 6
Australia 2 2 3 7
Belarus 2 2 3 7
Hungary 2 2 0 4
Austria 2 1 1 4
Finland 2 0 0 2
Turkey 1 2 2 5
Cyprus 1 2 0 3
Czech Republic 1 1 2 4
Slovakia 1 1 1 3
Morocco 1 1 0 2
Slovenia 1 1 0 2
North Korea 1 0 2 3
Britain 1 0 2 3
Romania 1 0 2 3
India 1 0 1 2
Latvia 1 0 1 2
Lithuania 1 0 1 2
Switzerland 1 0 1 2
Algeria 1 0 0 1
Bulgaria 1 0 0 1
Cuba 1 0 0 1