Chopra, 23, managed a winning best of 87.58 metres to go one better than India's previous best -- two silver medals in the 200m and now-defunct 200m hurdles at the 1900 Paris Games by British-Indian Norman Pritchard.
Hundreds of people watched the javelin final on a screen outside Chopra's house in Panipat in the northern state of Haryana, exploding with joy when the Indian was declared the winner.
The Czech Republic filled out the podium at Tokyo's Olympic Stadium, Jakub Vadlejch taking silver with 86.67m and Vitezslav Vesely claiming bronze with 85.44m.
Bollywood music boomed out on the stadium tannoy after Chopra had launched his sixth and final throw, in the knowledge he had won gold.
The farmer's son sprinted the length of the infield, an Indian flag fluttering over his shoulders.
"It feels unbelievable," Chopra said. "It is the first time India has won a gold in athletics, so I feel very good. We have just one gold here in other sports.
"This is our first Olympic medal for a very long time, and in athletics it is the first time we have gold, so it's a proud moment for me and my country."
Chopra added: "In the qualification round I threw very well so I knew I could do better in the final. I didn't know it would be gold, but I am very happy."
Sports Minister Anurag Thakur hailed the "golden boy" on Twitter within minutes of the triumph.
"India's Olympic History has been scripted! Your superbly soaring throw deserves a Billion cheers!" he said.
Chopra is only the second Indian in any sport to win an individual gold since Abhinav Bindra took the 10 metre air rifle title in 2008.
Chopra had came into the Olympics with the fourth best throw of the year and lived up to his form as a faltering Johannes Vetter of Germany struggled and failed to qualify as one of the top eight.
Vetter, who threw seven times over 90m between April and June, including a season's best of 96.29m, eventually finished down in ninth.
"It was a tough competition," the 28-year-old said, complaining that he was having problems not over-running his launch on the surface.
"If you watch the throws again, you can see it's not the right surface for me. It's a good surface for all the runners, for all the nice world records and Olympic records on the track, but not for a javelin thrower like me. So it really makes me sad."
Vetter added: "It's like driving a car on autopilot. You can't brake, and I have to brake to throw far.
Chopra, Vetter said, had done a "good job".
"He's a really talented guy, always really friendly," the German said.