Gauff, 15, reached the Wimbledon main draw through qualifying then upset five-time champion Venus Williams in the first round before falling to eventual champion Simona Halep in the fourth round.
Gauff is joined by four other teenagers among eight wildcard invitees: a trio of 17-year-old Americans in Caty McNally, Whitney Osuigwe and Katie Volynets and 16-year-old French player Diane Parry.
Stosur, meanwhile, brings a veteran presence. The 35-year-old Aussie won the title in Flushing Meadows in 2011 and has reached the quarter-finals on two other occasions.
Other women's wildcards went to former US collegiate champion Francesca Di Lorenzo and three-time Stanford University All-American and New Jersey native Kristie Ahn.
On the men's side, Americans Bjorn Fratangelo, Marcos Giron, Denis Kudla and Jack Sock join US Open Wild Card Challenge winner Ernesto Escobedo and 2019 US Tennis Association Boys’ 18s National Champion Zachary Svajda as main draw wild card recipients.
Antoine Hoang was awarded a main draw wildcard by the French Tennis Federation as part of its reciprocal agreement with the USTA, and Tennis Australia’s reciprocal agreement main draw wild card will go to a player to be announced.