Darvish was born in Habikino, Osaka, to an Iranian father, Farsad Darvishsefat, and a Japanese mother, Ikuyo. His parents met at Eckerd College, a liberal arts school in St. Petersburg, Florida, where his father played for the college soccer team. His grandfather owned a travel agency in Iran, and decided to send his son Farsad to the United States in 1977 to attend high school in Berkshire County, Massachusetts, where he also raced competitively in motocross.
Yu Darvish began playing baseball in second grade and led his team to the quarter-finals of the national tournament as well as a third-place finish in the international tournament as a member of the Habikino Boys. He was scouted by over 50 high schools while in junior high. He opted to attend Tohoku High School in northern Sendai, a noted baseball powerhouse that produced players such as former Seattle Mariners and Yokohama BayStars closer Kazuhiro Sasaki and former Arizona Diamondbacks reliever Takashi Saito.