After holding office as Deputy Chief Cabinet Secretary from 1984-1985, Taku Yamasaki served as Director-General of the Japan Defense Agency (防衛庁) in 1989, and then Minister of Construction from 1991-1992. He was also a member of the House of Representatives from 1972-2003 and again from 2005-2009.

After he lost his seat in the Diet, Yamasaki served as Special Advisor to a private research group on the constitution organized by the LDP at then-Prime Minister Junichirō Koizumi’s arrangement. He belongs to the Liberal Democratic Party (LDP), and he served as Secretary-General and Vice President of the LDP during the Koizumi administration.

In 2001, he published a book to propose his constitutional revision ideas. In the book, Yamasaki suggested that the preamble mention both "the Emperor" and "the people"; Japan exercise the right to collective self-defense for emergencies in areas around Japan (周辺事態) and Japan contribute to UN peacekeeping (PKO) operations to maintain international peace and security; and new clauses regarding environmental rights and rights to privacy be added.