Earlier the Belgian number one David Goffin quelled the challenge of his French counterpart Jo-Wilfried Tsonga 7-5 6-3 6-2.
“Jo started really powerfully,” said Goffin. “But I stayed with him and once I had got the first set I started to play better.”
The win in just under three hours levelled the tie at 2-2 and brought the number two players from each side to the fore to battle for the decisive point.
On paper there was no contest. Pouille, 23, is ranked 18th in the men’s hierarchy. Darcis, 33, is nearly 60 places beneath him.
But the veteran went into the clash with a fearsome reputation in the fifth match of Davis Cup ties. He had won on all five of the occasions that he had competed for the final point. The French were also bearing the weight of lost finals in 2002, 2010 and 2014.
Darcis started confidently. But from 40-0 in his opening service game, he dropped his serve. And he never recovered. Pouille, humbled on the opening day by Goffin, bristled muscularity and purpose. If the disparity was slight in the first set, it became heavy in the second. Darcis made the movements but there was no ballast or penetration.
With Pouille two sets up, the partisans sensed victory was imminent. Before the start of the third set they burst into a rendition of the French national anthem.
About 30 minutes later, they were belting it out again as team captain Yannick Noah stood among the men who had played for him during the 2017 Davis Cup campaign on the victory podium.
"In sports, it's never nice to be second," said Belgium skipper Johan Van Herck. "I am proud of my whole team. It was not about one player, it was about the whole team."
Despite Van Herck's protestations to the contrary, Belgium only had a chance of glory due to Goffin. He played sumptuous tennis in both of his matches. He was the highest ranked singles player at the tournament and justified his billing with clinical destructions of both of his adversaries.
"Goffin against Tsonga was an incredible match," said Noah. "Especially the first set. Jo didn't play badly in the match, it was just that Goffin was really good."
Noah added: "I'm happy for the whole team. It's tough when you haven't won the trophy for 16 years. Everyone gets used to losing. I got fed up with that culture because sometimes you are battling with people in your own camp.
"It's difficult to find the right words because it's difficult to express how much we've been dreaming about winning this trophy."