Gabby Williams scored 18 points to lead France, taking over in the extra session as the 2024 Games' hosts followed their male counterparts in reaching the final.
On Sunday they'll face a US team gunning for an unprecedented eighth straight Olympic crown.
"This is a once-in-a-lifetime opportunity and I'm so happy," Williams said. "This country, this federation, they've given so much to me. We've sacrificed a lot for each other, so the fact we can share this moment together... once in a lifetime, I'm so happy."
Williams, held in check early by Belgium, proved the difference maker when it mattered, converting a three-point play when she was fouled on a layup to get France off on the right foot in overtime.
Emma Meesseman pulled Belgium within one at 76-75, but Williams hit another layup then made a pair of free throws to give France some breathing room and after Janelle Salaun made a final free throw in the final second the Bercy Arena crowd erupted in joy.
"I'm glad the game went this way because it's going to be a game we never forget, the country of France will never forget," Williams said. "It's kind of fun to win games that are a little ugly, a little intense."
It was another bitter disappointment for European champions Belgium, who lost their quarter-final at the pandemic-delayed Tokyo Games by one point in their first Olympic appearance.
Belgium had the edge in a fast-paced first half, Elise Ramette leading the way as the Cats connected on 50 percent of their shots from the floor and kept French scoring threats Marine Johannes and Gabby Williams in check.
Valeriane Ayayi kept France in it, giving them their first lead with a pair of free-throws in the second quarter then producing a three-pointer and a driving layup to push the advantage to 29-18.
But with France connecting on just 26.5 percent of their shots in the first half the momentum soon swung Belgium's way and a 22-0 scoring run bridging the second and third quarters saw them surge to a 46-31 lead before Williams stopped the rot with a layup.
France, with 17 points from Ayayi and 15 from Iliana Rupert, chipped away and went into the fourth period training 51-48 after a pair of free throws from Williams to end the third.
Two more free throws from Rupert gave them a 52-51 lead and they stretched the margin to as many as six.
Belgium weren't done, however. Julie Vanloo, fouled on an attempt from beyond the arc, made all three free throws and Meesseman drained a three-pointer that was enough to force overtime.
Now they'll face Australia for bronze on Sunday.
"We tried," Meesseman said. "I think we came up short in some moments. We were not consistent enough."
