The 32-year-old led Serbia to victory in Sydney, Australia – first against old opponent Rafael Nadal and then against Victor Troicki.
Djokovic prevailed against Pablo Carreno Busta and Feliciano Lopez from Spain until the early morning hours in Australia.
"I will remember this experience as one of the best moments of my career for the rest of my life," said Djokovic.
"I was very happy and lucky to have had a great career in the past 15 years, but playing for the country with some of my best friends … you can't keep up with that. It's just too special."
Avenging defeat last year
At an emotional press conference last November, Troicki spoke about letting the team down after Serbia left Russia for the Davis Cup quarter-finals.
He and Djokovic had lost the double that day even though they had three match balls.
The new ATP Cup final gave Troicki and his teammates the opportunity to quickly remedy the situation – and to go down in history as the first winner of the tournament.
"I want to thank Novak for playing with me again," said Troicki. "I remember playing with him since we were nine or ten years old. I can't describe it in words to share such a moment with him in court.
"As you said, I will remember it for the rest of my life."
Fans may have been denied a blockbuster finale they could remember after Nadal made the double.
The player in first place in the world rankings lost again on hard court against Djokovic with 6: 2, 7: 6 (4). Since winning the US Open 2013, Nadal Djokovic has not hit hard court.
"I've played a lot of tennis in the past few days," said Nadal. "My energy level is slightly lower than usual."
The Spaniard had also spoken of waking up very early when his body clock adjusted to the Australian time zone.
The ATP will donate $ 500,000 to forest fire relief
After the final, ATP announced a $ 500,000 donation to the WWF's Australian Wildlife and Nature Recovery Fund.
The money was donated by the players on the men's tour after the forest fires that devastated Australia.
"Australia feels at home for us at the beginning of every season," said Djokovic. "It was devastating to see the damage that the bush fires have caused to wildlife and nature."