The shaven-headed Romanian turned around motionless after he completed his final shot, oblivious to the capacity crowd's cheers at the Royal Artillery Barracks' indoor range with his earplugs in.
"No I didn't know (I had won) I think the Italian coach told me," Moldoveanu told reporters. "I'm overwhelmed, I cannot describe it in words. It is crazy."
Moldoveanu was commanding and consistent as he finished with a total of 702.1 points, with Italy's Niccolo Campriani on 701.5 and Indian Gagan Narang on 701.1.
Expectations for the 29-year-old world number 34 were low after he had done little of note following his fourth place finish at the Beijing Games.
But he finished qualifying in second earlier on Monday with an Olympic record equalling 599 total from the 600 available along with Campriani.
The scoring was too tough for defending Olympic champion Abhinav Bindra, who could only finish 16th in the 47-man field with a total of 594, three points short of a place in the final.
Moldoveanu, who has a psychology degree, took an early lead in the eight-man final, where shooters fire 10 shots aiming for a maximum score of 10.9 with each.
Always the last to fire as he took most of the 75 second shot time to steady his arm, Moldoveanu began with five scores of 10.1 or better to take a 0.6 point lead over world number one Campriani.
But his worst score of the final, a 9.9, followed in the sixth as Campriani soared ahead with two scores of 10.8 before the pressure hit the Italian in the eighth.
Campriani could only manage a 9.9 and then a 9.4 as Moldoveanu wrestled back the lead with a closing run of four scores of 10.3 or above to seal a victory he didn't know he had.
"I didn't know (the score). You don't realise. You just focus and don't hear anything," Moldoveanu said.
"This is the way the sport is, it doesn't matter how you are in the world rankings it is just on the day that matters."
American-based Campriani, who will compete in two other rifle events in London, was pleased with his efforts in a high-quality final where Peter Hellenbrand of Netherlands scored the first 10.9 of the London Games.
"There was a lot of pressure and of course I am happy with the medal but I'm also very happy I got the job done," Campriani said.
There was joy for India also after Bindra's disappointing early exit when Narang finished with a 10.3 and then a 10.7 to snatch a bronze medal away from China's Wang Tao.
The burly Indian, who narrowly missed the final in Beijing, raised his gun above his head as his many compatriots in the crowd cheered loudly at the country's first medal of the Games.
"A bronze is very encouraging," Indian Sports Minister Ajay Maken told reporters. "It will help boost the moral of the Indian contingent and we have many good players who are medal hopefuls so we feel this is just the beginning."