Jin, who won the 10m Air Pistol event earlier this week, began this afternoon's final seven points behind fellow Republic of Korea athlete Choi Young Rae following the qualifying round.
The 32-year-old gradually cut into his team-mate's lead but with one shot remaining Choi was still 1.6 points ahead.
But Choi's nerve deserted him as he scored 8.1 while Jin nailed a 10.2 to claim the title in dramatic fashion.
Choi takes home silver, with China's Wang Zhiwei winning bronze.
Jin said: 'I knew if I won it would be second time that I had won this Olympic title, but I did not imagine I could do it.
'First qualifying was not going well so I almost gave up on that idea, I tried not to be too ambitious and just to do my best.
'As soon as the final was over I said sorry, but Choi said, "It's okay, I'm glad I got silver". But 30 minutes later he was saying, "I hate you".
'It's remarkable for Republic of Korea to get gold and silver but, for today at least, I feel sorry for Choi.'
America's Michael Diamond leads the way in qualifying for the men's Trap, scoring a perfect 75 for the first three rounds.
Two more rounds will take place tomorrow morning before the final in the afternoon, the last event of the shooting competition.
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