Following his graduation, Kobashi joined the Home Ministry and served as the director general of the Sanitary Affairs Bureau, director general of the Local Affairs Bureau, and director general of the Civil Engineering Bureau before finally assuming the post of Under-Secretary of Home Affairs on 25 April 1918.

He became a member of the Rikken Seiyūkai and was elected to the House of Representatives in 1920, serving three consecutive terms.

He resigned his position on 29 November 1929, following the Echigo Railway Scandal of which he was later acquitted.

[2] Kobashi died on 2 October 1939 in Tokyo, three weeks shy of his 69th birthday.

He was buried at Tama Cemetery and was posthumously awarded the Grand Cordon of the Order of the Rising Sun.