He was the first son of Yokoi Shonan, a scholar and political reformer during the end of the Bakufu era.

[1] In 1876, he moved to Tokyo and entered the Kaisei Gakko [ja], but quickly transferred to Doshisha University.

Yokoi graduated in 1879, was baptized by Joseph Hardy Neesima, and became a missionary in Imabari, Ehime.

After teaching at Doshisha University, he took over the Hongo Congregational Church in Tokyo from Ebina Danjo.

In 1897, Yokoi started the Hinototori Konwakai (丁酉懇話会),[4] and in the same year became president of the Doshisha School.