In the latter role, he worked closely with LDP Cabinet ministers Nobuteru Ishihara, Kazuyoshi Kaneko, and Seiichiro Murakami on administrative reform efforts.

[7] He chose to run as a DPJ candidate despite having recently worked in incumbent LDP Prime Minister Junichiro Koizumi's Cabinet Office.

[6] In his second electoral attempt in the 2009 general election, he won a seat representing the Kagawa 2nd district, and the DPJ took over the reins of government from the LDP.

With no single party reaching a majority, the DPFP, holding 28 seats, has become crucial in determining the balance of power.

Although he received overtures from both Shigeru Ishiba and Yoshihiko Noda, he declined to join a coalition government, emphasizing a stance of deciding on each policy on a case-by-case basis.

[23] On 4 January 2023, Tamaki visited Ise Grand Shrine on the same day as Prime Minister Fumio Kishida and CDP leader Kenta Izumi.

[24] In November 2024, Tamaki acknowledged entering into an extramarital relationship and apologized after the weekly magazine Flash reported that he was seen in hotels in Takamatsu with a local tourism ambassador.