He became interested in stage plays at an early age, largely due to the influence of his grandmother, who also provided financial support for him to attend college.

Kubota went on to write many full-length novels, including Tsuyushiba ("Dew on the Grass"), and Shundei ("Spring Thaw"), which depicted the joys and sorrows and traditional lifestyle of ordinary people in working-class neighborhoods in old pre-war Tokyo.

In the Great Kantō earthquake of 1923, his home in the Nippori neighborhood of Tokyo burned down, and he relocated to nearby Tabuchi, where he made the acquaintance of Ryūnosuke Akutagawa.

In 1926, along with the novelist Masao Kume, he joined the Tokyo Central Broadcasting Station (now NHK), and later headed the drama and music department.

In 1936, he accepted an assignment from the Tokyo Nichi Nichi Shimbun, sponsored by the Japanese Government Railways to tour the national parks of Japan In 1937, together with Kunio Kishida and Toyoo Iwata, Kubota created the Bungakuza theater company, promoting shingeki drama, and became a leading figure in the modern theater circles in Japan.

His funeral was held at the Tsukiji Hongan-ji, and his grave is located at the temple of Kifuku-ji in the Hongō neighborhood of Tokyo, behind the library of Keio University.