A native of Ōchi District, Shimane, he attended Tokyo Institute of Technology as an undergraduate studying applied physics, graduating in 1976, and received a Ph.D. in engineering from the same school.

[1] Saito is known for his ties with NASA as well as expert knowledge of lunar bases and clean energy technology.

Due to his knowledge in these areas, he was appointed parliamentary secretary of science and technology in 1999 in the Keizo Obuchi administration.

[2] In the Cabinet of Prime Minister Tarō Asō, appointed on 24 September 2008, Saito was retained in his post.

[3] On 9 November 2024, Saito was selected as leader of Komeito following an extraordinary party convention to replace Keiichi Ishii, who lost his parliamentary seat in the 2024 Japanese general election.