After returning to Japan in 1911, Uehara worked as lecturer on political science at Meiji University, Rikkyo University and at the forerunner of Tokyo Institute of Technology in Tokyo, teaching both comparative legal theory and constitutional law.

A supporter of the reforms of Inukai Tsuyoshi, he later changed party affiliations to the Rikken Seiyūkai.

In the 1939 schism of the Rikken Seiyuto, Uehara sided with the "orthodox" faction led by Ichirō Hatoyama.

After the end of World War II, Uehara helped form the Japan Liberal Party 1942–1948 together with Hatoyama and Hitoshi Ashida.

Despite his liberal credentials, he was highly opposed to Article 9 of the new Constitution of Japan, which he felt to be incompatible with a sovereign nation.