It is the first business in Cornwall for Britain's fastest growing restaurant and bar company.
The New York Italian restaurant opened at White River Place, next to White River Cinema.
Manager Mark Anderson said: "We are delighted to open our doors in St Austell.
"We know we offer the right mix of fun with a warm and friendly atmosphere which appeals to families and couples alike."
Sean Finlay, director of White River Developments said: "The opening of Frankie and Benny's this weekend marked an exciting landmark in the development of White River Place."