Yamaguchi won the 1963 Naoki Prize for his novel, Eburi Man shi no yūga na seikatsu (江分利満氏の優雅な生活) ("The Refined Lifestyle of Mr. Everyman"), which appeared serialized in the women's monthly magazine, Fujin Gahō, from 1961 to 1962.

This story about an average white-collar worker in Tokyo set the tone for many of his future works, which mock the new affluence of urban society in the 1960s, in contrast to the bitter war and post-war period.

Other noted works are: Majime ningen ("A Serious Person"), Izakaya Choji, Ketsu zoku ("Blood Relations"), Kazoku (Family) and Waga machi ("Our Town").

Yamaguchi also wrote a biography on Yoshino Hideo, in which he describes his own experiences during the period he lived in Kamakura, in the house next door to Kawabata Yasunari from 1945 to 1948.

Dansei jishin ("Man Himself"), a series of witty essays about the joys and sorrows of everyday life, was serialized in the weekly magazine, Shukan Shincho, from 1963 until his death in 1995 for a total of 1,614 episodes.