Before entering politics Matsui was a bureaucrat in the Ministry of International Trade and Industry.

While being a student he read the novel The Summer of Bureaucrats (官僚たちの夏) by Saburo Shiroyama, which inspired him to join the Ministry of International Trade and Industry when he graduated in 1983.

[1] While in the ministry Matsui was sent to the Kellogg School of Management at Northwestern University in the United States for further education and earned an MBA in 1990.

[3] When the DPJ took power in the 2009 House of Representatives election, Matsui was appointed Deputy Chief Cabinet Secretary under Prime Minister Yukio Hatoyama.

He was also endorsed by outgoing Mayor Daisaku Kadokawa and the Governor of Kyoto Prefecture Takatoshi Nishiwaki.