Indonesian political party formed in 1973 through the forced merger of five non-Islamic political parties. In the final three decades of the 20th century, it was one of two opposition parties officially recognized by the government, and though it often was supportive of the policies of President Suharto, its antigovernment faction, led by Megawati Sukarnoputri (Sukarnoputri, Megawati), was instrumental in Suharto's fall from power in 1998.

In 1973 Suharto's authoritarian regime implemented political reforms to limit the power of opposition groups and the number of recognized political entities to three: Golkar, a pro-government group that controlled state institutions, and two opposition parties, the Indonesian Democratic Party (later the PDIP) and the United Development Party. The Indonesian Democratic Party was created from three nationalist groups and two Christian-based parties: the Indonesian Nationalist Party, the Movement for the Defense of Indonesian Independence, the People's Party, the Catholic Party, and the Christian Party. The uneasy merger of groups that did not share a coherent political ideology resulted in poor electoral performances that prompted the government, fearing that the Muslim-based United Development Party might pose a threat to its rule should it become the sole opposition party, to intervene to strengthen its support.

In the 1980s and early '90s, the Indonesian Democratic Party rapidly expanded its vote share by appealing to voters frustrated by apparent inequalities in Indonesia's social and economic structure. Because the party blamed the country's social ills on the governing regime, Suharto attempted to undermine it. When the party selected Sukarnoputri, Sukarno's daughter, as its leader, the government engineered her removal with the aid of a faction opposed to her. Her dismissal precipitated mass protests and violence in Jakarta, and Sukarnoputri and her supporters eventually established a new political party, the PDIP, to challenge the government. In 1999 the PDIP became the largest in the legislature, and in 2001 Sukarnoputri was elected Indonesia's president. In 2004, however, Sukarnoputri was defeated in her bid for reelection, and the PDIP was supplanted by Golkar as the largest party in the legislature.