日本新党
Kaieda worked as an economic analyst and secretary to a member of the House of Councillors before winning election to the House of Representatives in the 1993 general election. He was originally a member of the Japan New Party, then formed a short-lived party following the JNP's collapse, and was one of the founding members of the Democratic Party of Japan in 1996. He retained a seat in the Tokyo proportional representation block in the 1996 general election, losing his Tokyo 1st district seat to Kaoru Yosano of the LDP. He regained his district seat in the 2000 election and 2003 election, but was forced out of the House of Representatives in the 2005 election, both losing his district seat to Yosano and failing to win a PR seat.