The 2011 US Open winner, who withdrew from consideration last year as she struggled for form and fitness, will provide valuable experience to a team led by world No 9 Ashleigh Barty.
Daria Gavrilova and Priscilla Hon were also selected for the April 20-21 showdown at Pat Rafter Arena in Brisbane.
Stosur is expected to play doubles, but she also holds the record for the most Australia Fed Cup singles wins.
Belarus has yet to name its team but it is set to be spearheaded by world No 10 Aryna Sabalenka, two-time Australian Open champion Victoria Azarenka and 35th-ranked Aliaksandra Sasnovich.
“She (Barty) is one of the world’s best Fed Cup players with her versatility in singles and doubles, and a great leader and asset to the team,” said team captain Alicia Molik.
“It’s also exciting to welcome Sam back into the team, she has a really strong Fed Cup record and her recent doubles results are unparallelled, and Dasha and Pri are both great team players.”
Australia is looking to reach its first Fed Cup final since 1993 and reclaim the title they won by beating the United States in 1974.
The other semi-final is between France and Romania.