Les Bleus fell behind to first-half efforts from Yannick Carrasco and Romelu Lukaku in Turin, but two goals in six minutes after the break, from Karim Benzema and a Kylian Mbappe penalty, hauled the French back into the game and set up a grandstand finish.
Theo Hernandez delivered the winner in the 90th minute, netting his first international goal to send France into a final against Spain in Milan on Sunday.
“We were unhappy in the first half,” Deschamps told TF1. “They managed to score two goals in their good 20-minute period. Then we were hardly in danger and we had a lot of chances.
“Our system is new, we need time to work on it, and the opponent was good.
“Winning this match in that way proves the strength of character of this team. They are there and they do not want to let go.
“We are here to play the final and there will be a trophy at stake. We’ll do everything we can in order to lift it.”
The consolation for Belgium is a third-place play-off against Euro 2020 winners Italy in Turin on the same day as the final.
“Our first half was really extraordinary,” said Red Devils boss Roberto Martinez, in quotes reported by L’Equipe. “We were so confident.
“In the second half we were a little too emotional. Maybe we were thinking a little too much about the final, about qualifying. We didn’t do what we had to do. We let France come back into the match and they had the energy to score one last goal.
“But I still find it very cruel to lose a match like that, in the 90th minute, given our first-half performance. We must applaud the application of the players in the first half.
“It’s a good time for us now to show our resilience in the third-place play-off against Italy. In 13 months there will be a World Cup and each match must be an opportunity to show our level.”