Born in Santa Ana, California, Ishii received an Associate of Science degree from Reedley Junior College in 1966, a Doctor of Pharmacy from the University of the Pacific School of Pharmacy in 1970, and a Juris Doctor from the University of California, Berkeley, Boalt Hall School of Law in 1973.

He was a deputy in the City Attorney's Office of Sacramento, California in 1975, and a deputy public defender, Public Defender's Office, County of Fresno, California in 1979.

On February 12, 1997, Ishii was nominated by President Bill Clinton to a seat on the United States District Court for the Eastern District of California vacated by Robert E. Coyle.

Ishii was confirmed by the United States Senate on October 9, 1997, and received his commission on October 14, 1997, becoming the first Asian Pacific American judge on the United States District Court for the Eastern District of California.

In 2013 Ishii received the President's Award from the Asian/Pacific Bar Association of Sacramento.