Noguchi was born in Japan and graduated from Tokyo’s Nippon Medical School in 1951 before interning at The University of Tokyo School of Medicine Hospital. Shortly thereafter he immigrated to the United States. He then served a second internship at Orange County General Hospital and a series of residencies at Loma Linda University School of Medicine, and Barlow Sanatorium in Los Angeles. He was appointed a deputy coroner for Los Angeles County in 1961.

          In 1967, he became Chief Medical Examiner (CME) for the county, replacing his mentor Theodore Curphey. It was in this role that Noguchi came to public attention for a series of autopsies he either performed or supervised on a range of celebrities and public figures that included Marilyn Monroe, Robert F. Kennedy, Janis Joplin, Albert Dekker, William Holden, John Belushi, Natalie Wood, Sharon Tate, and Gia Scala. His autopsy of Kennedy is significant for its conclusion that the fatal shot was fired into the back of Kennedy’s head, behind the right ear, from an upward angle, and from a distance of no more than one-and-a-half to three inches away. This has given rise to conspiracy theories regarding the assassination, as no witnesses reported seeing the convicted assassin, Sirhan Sirhan, in a position to fire such a shot. Noguchi himself points out, in his memoir Coroner, that he has never officially ruled that Sirhan fired the fatal shot.