He was born in Fukuoka Prefecture and graduated from La Salle junior/senior high school in Kagoshima. He attended Waseda University and earned a Master's degree from Kyoto University. Yoshida died of a lung blockage in 2004.

Yoshida was known primarily for "Light novels," a category in Japanese publishing that includes youth-oriented stories, often featuring anime-style cover illustrations.

In 1997, Yoshida was awarded the Sneaker Taisho literary prize for his debut novel, Genocide Angel. He was the author of the novel series Trinity Blood, which was serialized in Kadokawa Shoten's The Sneaker magazine. The popularity of The Sneaker dropped significantly after Yoshida's death. The Trinity Blood series was published in North America by Tokyopop.

Two years after Yoshida's death, from January to October of 2006, his home village of Ashiyamachi, Fukuoka, in conjunction with publishers Kadokawa Shoten, Gonzo and Broccoli, held a "Sunao Exhibit" to memorialize his achievements.

Gainax's scheduled project Bushilord was indefinitely delayed after his death, as he was supposed to be it's world designer.