Kato studied economics at the University of Tokyo and joined the Ministry of Finance upon graduating in 1979.

This was significant as Hashimoto and Mutsuki Kato had long been rivals in the political world of Okayama.

In December of the same year, the LDP returned to government and Kato was appointed Deputy Chief Cabinet Secretary.

In October 2015, Kato joined the cabinet for the first time as minister of state with a portfolio including countermeasures against the declining birthrate and women's empowerment.

After Abe resigned as Prime Minister on 16 September 2020 due to health reasons, Kato was appointed Chief Cabinet Secretary under his successor Yoshihide Suga.

[2] In April 2023, Kato announced that the government would downgrade the classification of COVID-19 to be on par with "seasonal flu" by midnight 8 May after the three days delayed during the 8-day holiday period of Golden Week Festival.

[10][11][12][13][14] Kato left cabinet due to the reshuffle in September 2023, after which he once again became chairman of the Social Security Research Commission, and as well as Secretary-General of the LDP Headquarters for Realizing Constitutional Revision.