Before his involvement in electoral politics, Miyashita worked for the Ministry of Land, Infrastructure, Transport and Tourism and was employed at the Consulate General of Japan, New York City.

[1] Upon graduating university, Miyashita was employed by the Ministry of Land, Infrastructure, Transport and Tourism and oversaw the Tohoku Regional Development Bureau.

[5][6] On March 3rd, 2023, Miyashita resigned as mayor in order to pursue his candidacy in the 2023 Aomori gubernatorial election.

[7] While serving as mayor of Mutsu, Miyashita had announced his candidacy for the 2023 Aomori gubernatorial election on January 6, 2023 at a press conference meeting.

[8] In the election, Miyashita achieved a victory over his opponent, former mayor of Aomori City, Akihiko Onodera.