Yamaguchi was born and raised in Tokyo, Japan. His Hawaiian roots are tied to his paternal grandfather who owned a tavern in Wailuku, Maui in the 1940s. He attributes his appreciation for food to his Hawaii-born father and his Okinawa-born mother. Upon graduating from high school, Yamaguchi enrolled in the Culinary Institute of America (CIA) in New York where he received his formal culinary training. After graduating in 1976, he accepted positions at California restaurants including L'Escoffier, L'Ermitage, Le Serene, Michael's, and Le Gourmet in the Sheraton Plaza La Reina. In 1984, Yamaguchi opened his first restaurant, 385 North, in Hollywood. In 1988, he moved to Honolulu to open the first Roy's Restaurant. Since that time, he has opened 29 restaurants in the United States, as well as others in Japan, Guam, and Hong Kong. He also teamed with Outback Steakhouse to open a Eurasian-themed restaurant in Florida.