He is known for Hawaiian-inspired cuisine, an eclectic blend of California-French-Japanese cooking traditions created with fresh ingredients from the Islands.

His Hawaiian roots are tied to his paternal grandfather, who owned a tavern in Wailuku, Maui, in the 1940s.

In addition, Yamaguchi founded and chairs, along with Chef Alan Wong, the Hawaii Food & Wine Festival.

[12] Founding the Roy's Annual Golf Classic more than 17 years ago, Yamaguchi has been instrumental in raising more than $400,000 for Imua Family Service.

[citation needed] In 2000, Yamaguchi sold the interest in the mainland US locations of Roy's Seafood restaurants to Bloomin' Brands, parent of Outback Steakhouse.

In 2015, Bloomin' Brands sold the mainland US Roy's operations to United Ohana for $10,000,000 US (approx.