Born in Dalian, Kwantung Leased Territory, he graduated from high school in Kitakyushu, Fukuoka Prefecture, Japan.
A member of the 13th group of actors and actresses trained at the Haiyū-za, he counts Tetsuo Ishidate, Toshiyuki Hosokawa, Tomomi Satō, and Gō Katō as classmates.
Another major jidaigeki role began in 1978 as Yokouchi played the historical Ōoka Tadasuke in Abarenbo Shogun (TV Asahi).
He appeared in the 1980 Shishi no Jidai starring Bunta Sugawara, and as Shimizu Yoshimasa in the 2007 Fūrin Kazan, having been in the 1992 Nippon Television show of the same name.
A versatile talent, Yokouchi has also appeared in contemporary dramas, dubbed foreign productions, and voiced animated characters.