Melanie Segard, 21, will begin training for the broadcast next Tuesday at the studios of public television station France 2, UNAPEI said in a statement.
Segard has scored more than 200,000 "likes" on Facebook in less than two weeks since the association launched a public awareness campaign for Down's Syndrome titled "Melanie Can Do It".
"Hi everyone, my name is Melanie and my dream is to present the weather," she says in the post.
A France 2 presenter, Chloe Nabedian, noticed the story on social media and suggested it to the channel's weather service. "It just seemed obvious to us," said Nathalie Rihouet, who runs the service for France 2 and France 3. "We're going to get everything in place so that she is at her best."
"Seeing the public rally spontaneously around Melanie gives hope to thousands of people with disabilities who are still too often invisible," added the statement by UNAPEI.
Down's Syndrome is a genetic condition with no known cure that typically affects a person's physical and intellectual growth.
It affects approximately one in 1,000 people, according to the World Health Organization.
Also known as trisomy 21, the condition is caused by the presence of an extra, or third, copy of chromosome number 21.
"Melanie is our ambassador," UNAPEI president Luc Gateau told French radio. "We have just proved that a person with a handicap can realise her dream," he said, adding: "Society needs this."