A native of Ibaraki Prefecture and graduate of the University of Tokyo he joined the National Police Agency in 1982 becoming the director in the Juvenile Community Safety division.

After leaving the agency in 1999, he was elected to public office for the first time in 2003 representing Ibaraki 3rd district, which includes the cities of Ryugasaki and Ushiku, among others.

Hanashi resigned as Justice Minister on 11 November 2022 following comments he made to a political gathering earlier in the week suggesting that the Justice Minister was a “unspectacular position” that became "a top story in daytime news programs only when stamping a seal on documents of execution."

and “Serving as justice minister won't help raise much money or secure many votes”.

Opposition leaders like Akira Koike of the Japanese Communist Party said that Hanashi was disrespecting the post and its responsibilities, as well as making light of the death penalty.