Ustyugov, a soldier competing in his first Games, cruised across the finish line at the Whistler Olympic Park in 35 minutes 35.7 seconds, 10.5 seconds ahead of Frenchman Martin Fourcade.
Ustyugov's triumph ended a 16-year Olympic biathlon gold medal drought for Russian men. The 24-year-old raised his arms to wild cheers from flag-waving Russians as he crossed the line.
"To be perfectly honest, I started out with negative thoughts because we haven't won anything in so long," said Ustyugov. "I realised it was high time we broke out of this vicious circle.
"And God smiled upon us today and I won gold."
Fourcade, 21, missed two targets in the opening stage and another in the final round to scupper his chances of catching Ustyugov.
He finished 6.1 seconds ahead of Slovakian Pavol Hurajt, who claimed bronze after leading for much of the race.
"The beginning was hard," said Fourcade, who blew kisses to the crowd as he approached the finish line with France's fifth biathlon medal in Vancouver.
"I missed two targets in my first prone and I said, 'Now it's finished and I can't go on the podium.' But I kept fighting because it was the Olympics.
"If you say you can't (go on the podium) everybody looks at you. You have to fight and it got better and better for me. I could see the other athletes were tired. Today was tough."
Ustyugov, ranked third in the World Cup overall standings, was 13th after the first shooting frame and moved up to seventh after the second.
He stalked the leaders, sitting in fourth place after the third round before moving up to second behind Hurajt when the last of four shooting sessions concluded.
Ustyugov found another gear to pass a badly tiring Hurajt who became the first Slovakian man to win an Olympic biathlon medal.
"I was disappointed after my last race, and I know that every shot counts," said Ustyugov. "But I couldn't see where the other athletes were so I just skied as strongly as I could.
"I only started to think about the gold medal when I got to the stadium and I could see the finish line."
Ten-times Olympic medallist Ole Einar Bjoerndalen of Norway missed seven targets, his worst shooting since a 1994 World Cup event in Oslo, and finished 27th in the 30-man field.
"On some days, it's just not working," said the 36-year-old Bjoerndalen. "Today certainly was a horrible day. I made seven mistakes at shooting. These Olympic Games are very disappointing for me. Horrible.
Bjoerndalen's compatriot, World Cup leader Emil Hegle Svendsen, winner of two medals in Vancouver, finished 13th after missing three targets.
Place of birth: Krasnoyarsk, Russia
No previous Olympic results
Best career achievement:
Sixth, 2009 world championships, 4x7.5km relay
Background: Ustyugov, who leads the overall World Cup standings this season, started competing in biathlon in 1997. He is educated in environmental engineering and enjoys downhill skiing and rock climbing.