James Yaegashi was born in Yokohama and raised in Yamagata to a Japanese father and an American mother. Upon graduating high school, he moved to America and majored in acting and directing at University of Missouri–Kansas City. He moved to New York with his wife in 1998.
He has acted in various stage productions including Mr. Yunioshi in a stage production of Breakfast at Tiffany's; a role that typically was renowned for being a whitewashed role. Of the character Yaegashi said "He’s a real character, for starters. The film...made so many changes to the story...Yunioshi is a Nisei, a Japanese American from California. In the movie, Mickey Rooney played him as if he was fresh off the boat." He ultimately felt it was necessary to play the character to portray ethnic characters in a positive light. Yaegashi first entered the Marvel Cinematic Universe with a minor role in Daredevil, but had a more notable role when he was cast as Robert Minoru in the Hulu original series Runaways based on the Marvel Comics series.