Australia had the overnight lead but world number 12 David Goffin narrowly overcame 20th-ranked Nick Kyrgios 6-7 (4-7) 6-4 6-4 6-4 as Belgium levelled.
Steve Darcis then saw off Jordan Thompson 6-4 7-5 6-2 for victory.
France booked a place in the final, which they will host, when Jo-Wilfried Tsonga beat Dusan Lajovic to give them an unassailable 3-1 lead over Serbia.
"It's a big win for me and a big win for us," said Darcis.
"David [Goffin] did an unbelievable job for us today. I have never seen him play as well as this and I'm really happy I could finish it off."
Nine-time champions France will play 2015 runners-up Belgium on 24-26 November.
Yannick Noah's side needed only one singles match on Sunday to see off a Serbian side who were without Novak Djokovic.
Underdogs Serbia had picked up an unexpected first point when Lucas Pouille lost to Lajovic in Friday's singles but Tsonga levelled by beating Davis Cup debutant Laslo Djere.
Pierre-Hugues Herbert and Nicolas Mahut then beat Filip Krajinovic and Nenad Zimonjic in the doubles and Tsonga's second victory saw them progress.
- Title: Davis Cup semi-finals: France to host Belgium in November final
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- Date: 1:14 PM