The Democratic Party of Japan (DPJ) was created in 1998, when reform-minded politicians from a number of opposition parties came together with the aim of establishing a genuine opposition force capable of taking power from the long-dominant Liberal Democratic Party (LDP). Former Prime Ministers Tsutomu Hata, Yukio Hatoyama and Naoto Kan were amongst those instrumental in establishing the new party. Since then the DPJ has grown in size at successive elections, and the party was further strengthened by a merger with the Liberal Party, led by Ichiro Ozawa, in 2003.

In contrast to the LDP, which has depended almost entirely on the bureaucracy for policy-making, the DPJ is a party dominated by young professionals, including bureaucrats, lawyers, doctors, aid workers, bankers, and journalists, who are able to draw on a wide variety of experience in formulating policy proposals. As a result, DPJ politicians have introduced a large number of independent members' bills. The party places a strong emphasis on the speedy implementation of across-the-board reform and the creation of a fairer and more inclusive social environment in Japan. The DPJ was instrumental in introducing the manifesto (party platform) to Japanese politics, marking the initiation of genuine policy debate.

The DPJ steadily increased its presence in both sides of the Diet and won a landslide victory in the 2009 general election, bringing about the first change of government in Japan under a two-party system since WWII. While in office, the DPJ focused on such issues as recovery and reconstruction following the Great East Japan Earthquake, revitalizing the national economy in the midst of the global economic crisis, and investing in Japan's future by carrying out comprehensive reform of the social security and taxation systems. Following defeat in the 2012 general election, the party has regrouped under the leadership of Banri Kaieda. The DPJ intends to continue to provide a viable alternative to the ruling coalition, and to work toward the implementation of policy goals that protect people's lives and livelihoods.