Jamaican Wayne Pinnock took silver with 8.36 and Italy's Mattia Furlani (8.34) claimed bronze.
The sombre world champion clinched the title with his second attempt and only cracked a grin once he was able to embrace his team in the stands before wrapping himself in the Greece flag.
Tentoglou is only the second man to retain his long jump title after American great Carl Lewis, who won from 1984-1996.
"This (title) is for my country. Greece is the country that invented the Olympics, so (I am) happy to do it for them," he said.
The world champion entered Paris in extraordinary form, having won all but one of the 11 competitions he had contested this season, but was second in the standings behind Italy's Furlani after a first attempt of 8.27.
Tentoglou stared solemnly down the runway before his winning leap, an effort that earned gasps from the crowd.
He chased a bit of insurance but could only reach 8.24 on the third attempt and clapped his hands in frustration as he landed at 8.36 on the fourth.
It did not matter, however, as Furlani could not improve on his opening jump and Pinnock took silver with his second attempt after finishing second at the World Championships in Budapest.
The Greek told reporters he had hoped to jump farther, calling it only a "decent" performance, even as his country's leaders leapt to congratulate him on social media.
"Mythical Miltos Tentoglou at the top of the world for one more time," Greek Prime Minister Kyriakos Mitsotakis wrote on the social media platform X.
President Katerina Sakellaropoulou added: "Tentoglou earned a well-deserved place in the pantheon of top long jump athletes."
