Natsuo Yamaguchi currently serves in the House of Councillors, having assumed office in 2001. He has also formerly served in the House of Representatives from 1990-1996.

As President of the New Komeito Party (公明党, Kōmeitō) since 2009, Yamaguchi has supported the party’s constitutional stance; Kōmeitō has proposed to “add” clauses instead of to modify the constitution, aiming to follow modern issues that did not exist when the constitution was written, such as protection of new human rights and expansion of local autonomy (2019 speech).