When Hamada expressed an interest in politics, Inagawa introduced him to the right-wing fixer Yoshio Kodama.

In July 1973 he took part in the formation of the Seirankai, a cross-factional right-wing group, along with Ichiro Nakagawa, Shintaro Ishihara, Michio Watanabe and others.

[2] During the intraparty "40-day war" which followed the October 1979 election, Hamada sided with incumbent Prime Minister Masayoshi Ohira.

In an incident that was caught on national television, Hamada kicked down barricades which non-mainstream LDP members had built to prevent a party meeting from renewing confidence in the prime minister.

[4] During the trial of Kenji Osano in connection to the Lockheed bribery scandals in March 1980, it was revealed that Hamada had lost almost two million American dollars playing baccarat in Las Vegas in October 1972.

In February the following year Hamada accused Japan Communist Party Chairman Kenji Miyamoto of being a murderer during a committee deliberation.

This referred to an incident in 1933, when an alleged police informant in the Communist Party had been found dead after interrogation by Miyamoto and others.

He didn't run in the 1993 election, handing over his position to his son Yasukazu Hamada, who had been his secretary since 1984, and retiring from politics.

[2][5] Kōichi Hamada died of heart failure on 5 August 2012, at the age of 83, in his hometown Aohori, now part of Futtsu in Chiba Prefecture.