Born in Tokyo and graduated from the Department of Imaging Arts and Sciences at Musashino Art University. While working as a web designer, he wrote Genocidal Organ and submitted to Komatsu Sakyō Award contest in 2006. Although it did not receive the award, it was published from Hayakawa Publishing in 2007 and was nominated to Nihon SF Taisho Award.

Since 2001, he had to be hospitalized frequently for recurrent cancer. He died at age 34 on March 20, 2009. The video game Metal Gear Solid: Peace Walker and the last chapter of the manga Aki Sora were dedicated to his memory.

A poll by the yearly science-fiction guidebook SF ga Yomitai ranked Genocidal Organ as the number one domestic sci-fi novel of the decade. Hayakawa's S-F Magazine All-Time Best poll in 2014 ranked Harmony as the top of the Japanese SF novels.

Toh Enjoe's Self-Reference ENGINE was also a finalist of Komatsu Sakyō Award and published from Hayakawa Shobō in 2007, along with Itoh's Genocidal Organ. Since then they often appeared together at science fiction conventions and interviews, and collaborated in a few works, until Itoh's death. At the press conference after the announcement of Enjoe's Akutagawa Prize in January 2012, Enjoe revealed the plan to complete Itoh's unfinished novel The Empire of Corpses. It was published in August 2012, and received the Special Award of Nihon SF Taisho Award.