Teagan Berry ranks third among the NRLW's leading try-scorers, with 40 tries from 52 appearances.
The 24-year-old fullback will leave St George and join Cronulla on a deal running through the 2028 season.
Berry will link with the Sharks for pre-season training in May before beginning her Cronulla career in 2027.
Her move follows a State of Origin debut for New South Wales, who won the series earlier this year.
Only Tamika Upton and Jessica Sergis have scored more NRLW tries than Berry.
Sharks coach Tony Herman said, "To have been able to secure the services of Teagan for two years is a great boost for the team going forward,"
"Teagan can play a number of positions in the backline, has great speed, an ability to find the try line, and she will be a tremendous asset to the team.
"We look forward to welcoming Teagan to the Sharks in 2027."
The South West Rocks product's versatility and attacking record were key factors in Cronulla's decision to sign her.