Oh's comfortable 7-1 victory over Japan's Takaharu Furukawa claimed a third title out of four at Lord's cricket ground for the dominant South Korean archers.
The country also won gold in the women's individual and women's team events and was the bronze medallist in the men's team.
Oh's victory in the last archery match at the London Games ended a long wait for South Korea's first individual men's Olympic title and delighted Korean fans after top seed and favourite Im Dong-hyun was surprisingly knocked out earlier Friday.
"My dream was to compete at this Olympics. On top of that I have a gold medal, so I am very happy man," said the third-seeded Oh, who was at his first games. "If you talk about the secret to strong archery in Korea, I don't know. But many Koreans are very strong at perseverance and I am one of them."
Dai Xiaoxiang of China took bronze with a come-from-behind 6-5 victory over Dutchman Rick van der Ven in the third-place match following a shoot-off. Having been 4-0 down, Dai hit a 10 in the sudden-death shoot-off at the end of the tense contest, piling the pressure on Van der Ven, who only managed an eight.
Dai had just missed out on a chance at gold, however, when he fell in a shoot-off to Oh in the semifinals.
"This is not what I wanted," Dai said of his bronze.
Top seed and new world record holder Im was beaten by Van der Ven in the last 16 earlier on the final day. Im set a 72-arrow world best in the Olympic ranking round last week but slipped up against Van der Ven, losing 7-1.
But Oh's win continued South Korea's dominance after Ki Bo-bae took women's individual gold Thursday to follow up on the gold and bronze in the team events. Oh was part of South Korea's men's team
"The first thing will be to have some time with my teammates ... and congratulate each other," Oh said after being asked about his celebration plans.
Oh was unworried for most of the final — played in bright sunshine and again in front of packed stands on the final day of archery at the famous cricket ground in north London. He won the opening two sets with 29 out of a possible 30 points in both.
Furukawa forced a tie in the third set, with the archers sharing the two set points to make it 5-1.
But Oh responded with a maximum 10-point shot in the middle of the target in the fourth set — one of seven for him in the gold medal match — to carry him to victory.
Furukawa had three 10s in the final for his silver.
"Immediately after I lost the final, I was not happy," he said. "But then after various interviews the feeling of happiness gradually came to the surface and now I'm really really happy."
Dutchman Van der Ven exceeded all expectations to make the last four after he only qualified for the Olympics in June.
He took an early lead in the bronze medal match, but China's Dai stormed back to win the third and fourth sets. The players shared the fifth, forcing the shoot-off, where Dai edged it for China's second medal in the archery.
South Korea topped the archery table with its three golds and a bronze. Italy was second after winning men's team gold, and China was third overall with a silver and Dai's bronze.