[2][3] In the 1958 Japanese general election, Aoki volunteered for Noboru Takeshita, a Waseda alumni who was running to represent Shimane for the Liberal Democratic Party.

Aoki was parliamentary secretary for the Ministry of Finance from 1991 to 1992 and chairman of the House of Councillors Committee on Agriculture, Forestry and Fisheries from 1994 to 1995.

The reshuffle in December of the following year made Aoki Chief Cabinet Secretary and Director-General of the Okinawa Development Agency.

Once it became clear Obuchi would not recover, Aoki met with the principal officers of the LDP at the time: Yoshiro Mori, Hiromu Nonaka, Shizuka Kamei and Masakuni Murakami.

[6][7] Mori initially retained the entire Obuchi cabinet, including Aoki, but after the reshuffle in December, he returned to his post as Secretary-General for the LDP in the House of Councillors.

[9] When Junichiro Koizumi succeeded Mori as Prime Minister, Nonaka took a confrontational stance while Aoki was cooperative.

In the 2003 LDP leadership election, Hiromu Nonaka endorsed Takao Fujii while Aoki supported the re-election of Koizumi.

In the 2018 LDP leadership election he endorsed Shigeru Ishiba against the incumbent Shinzo Abe, and requested his old faction to do the same.