Yanai is located in southeastern Yamaguchi Prefecture, at the base of the eastern coast of the Murotsu Peninsula.

Following the Meiji restoration, the village of Yanai within Kumage District, Yamaguchi was established with the creation of the modern municipalities system on April 1, 1889.

On March 31, 1951 Yanai annexed the villages of Hizumi, Shinjo, Yoda, and Iriku and was raised to city status.

Yanai has a mayor-council form of government with a directly elected mayor and a unicameral city council of 16 members.

In terms of national politics, the city is part of the Yamaguchi 2nd district of the lower house of the Diet of Japan.

Yanai has a rural economy based on agriculture (flowers and fruits), commercial fishing and food processing.