In 1969, Hata entered the House of Representatives of Japan, representing Nagano Prefecture as a member of the Liberal Democratic Party.
He rose to become a top lieutenant in the Tanaka/Takeshita faction in the 1980s.

In 1991, he served as Minister of Finance under Kiichi Miyazawa.
He left the LDP in 1993 to found the Japan Renewal Party with longtime LDP ally Ichirō Ozawa, which became part of Morihiro Hosokawa's anti-LDP coalition government later that year.
Hata served as foreign minister in the Hosokawa cabinet.

On 28 April 1994, Hosokawa resigned and Hata became prime minister.
However, the Japan Socialist Party had recently left the coalition, destroying its majority in the Diet.
Rather than face a vote of no confidence, Hata elected to resign in June, allowing SDP leader Tomiichi Murayama to take over the position on 30 June.

A number of progressive reforms were introduced during Hata's tenure as prime minister.
A law passed on 17 June 1994 to amend the Law concerning Stabilization of Employment for Older Persons aimed to encourage employers to plan continuous employment for older employees after the age of 60, as well as to prohibit employers from setting a compulsory retirement age lower than 60 and appoint public corporations as centres "for the practical use of older workers' experience."
On  22 June 1994, the Support Centre for Employment of the Disabled was established by law to provide practical advice, vocational training, and information to disabled workers and employers.
A health insurance amendment law passed on 29 June 1994 exempted employees from the requirement to pay National Health Insurance fees during child-care leave.

After the Shinseito merged into the Shinshinto in late 1994, Hata contested the leadership against Ichiro Ozawa.
After losing this contest, he and twelve other Diet members formed the splinter Sun Party (太陽党 Taiyōtō).
The Sun Party in January 1998 became a part of the Good Governance Party which itself was subsumed by the 
Democratic Party of Japan in April 1998.
In 1969, Hata entered the House of Representatives of Japan, representing Nagano Prefecture as a member of the Liberal Democratic Party. He rose to become a top lieutenant in the Tanaka/Takeshita faction in the 1980s.
In 1991, he served as Minister of Finance under Kiichi Miyazawa. He left the LDP in 1993 to found the Japan Renewal Party with longtime LDP ally Ichirō Ozawa, which became part of Morihiro Hosokawa's anti-LDP coalition government later that year. Hata served as foreign minister in the Hosokawa cabinet.
On 28 April 1994, Hosokawa resigned and Hata became prime minister. However, the Japan Socialist Party had recently left the coalition, destroying its majority in the Diet. Rather than face a vote of no confidence, Hata elected to resign in June, allowing SDP leader Tomiichi Murayama to take over the position on 30 June.
A number of progressive reforms were introduced during Hata's tenure as prime minister. A law passed on 17 June 1994 to amend the Law concerning Stabilization of Employment for Older Persons aimed to encourage employers to plan continuous employment for older employees after the age of 60, as well as to prohibit employers from setting a compulsory retirement age lower than 60 and appoint public corporations as centres "for the practical use of older workers' experience." On  22 June 1994, the Support Centre for Employment of the Disabled was established by law to provide practical advice, vocational training, and information to disabled workers and employers. A health insurance amendment law passed on 29 June 1994 exempted employees from the requirement to pay National Health Insurance fees during child-care leave.
After the Shinseito merged into the Shinshinto in late 1994, Hata contested the leadership against Ichiro Ozawa. After losing this contest, he and twelve other Diet members formed the splinter Sun Party (太陽党 Taiyōtō). The Sun Party in January 1998 became a part of the Good Governance Party which itself was subsumed by the 
Democratic Party of Japan in April 1998.
Tsutomu Hata