Created in February 1979 by clergy who had been students of Khomeini before his exile from the country in 1964, the IRP emerged as the country's dominant political force. Core members included ayatollahs Beheshti, Abdol-Karim Musavi-Ardabili, and Mohammad Reza Mahdavi-Kani and hojjatoleslams Khamenehi, Rafsanjani, and Bahonar. All had been active in mobilizing large crowds for the mass demonstrations during the Revolution. Following the overthrow of the shah, the IRP leaders continued to use their extensive contacts with religious leaders throughout the country to mobilize popular support. The IRP leaders perceived the secular, leftist, and more liberal Islamic parties as threats to their own political goals. As early as the summer of 1979, the IRP encouraged its supporters to attack political rallies and offices of these other parties.

Although Khomeini himself never became a member of the IRP, the party leaders exploited their close association with him to project a popular image of the IRP as the party following the line of the imam Khomeini. This implicit identification helped IRP candidates win a majority of seats in the elections for the Assembly of Experts that drafted the Constitution. During the 1980 elections for the first Majlis, IRP candidates and independents sympathetic with most IRP positions again won a majority of the seats. The party's effective control of the Majlis emboldened the IRP in its harassment of opponents. Throughout 1980 IRP-organized gangs of hezbollahis used intimidation tactics against supporters of other political parties, and consequently, most of the secular parties were cowed into silence as their leaders fled to foreign exile.

By 1981 the only political party that could seriously challenge the IRP was the Mojahedin. This Islamic organization had grown rapidly in two years from a few hundred supporters to a membership of 150,000, mostly educated young men and women in the cities, who were attracted by the Mojahedin's liberal, even radical, interpretations of traditional Shia concepts. The ideological conflict between the Mojahedin and the IRP was serious because the former rejected the IRP argument of a religious basis for the political principle of velayat-e faqih. In fact, in June 1980 Khomeini denounced the Mojahedin on account of the organization's insistence that laymen were as qualified as clergy to interpret religious doctrines. Although the Mojahedin closed most of its branch offices following this verbal assault, unlike the secular political parties it was not easily intimidated by IRP-organized political violence. On the contrary, Mojahedin members engaged in armed clashes with hezbollahis. Tensions between Mojahedin and IRP partisans intensified during the political conflict between Bani Sadr and the IRP leaders. The Mojahedin lent its support to the beleaguered president after Bani Sadr was impeached, the organization rose in armed rebellion against the IRP-dominated government.

Several of the small leftist parties joined the Mojahedin uprising. These included the Pay 1653 ykar, a prerevolutionary Marxist splinter from the Mojahedin, and the Fadayan Minority. The latter had split from the main Fadayan (thereafter referred to as the Fadayan Majority) in 1980 after a majority of the party's Central Committee had voted to support the government. Both the Paykar and the Fadayan Minority shared the view of the Mojahedin that the IRP was "merely a group of fascist clerics blocking a true revolution." The Mojahedin had a much broader base of support than did either of its allies, but the combined strength of all the parties could not match the capabilities of the IRP in terms of mobilizing masses of committed supporters. Thus, the government eventually was able to break the back of the armed opposition. The Mojahedin survived largely because its leader, Masud Rajavi, escaped to France, where he reorganized the party while in exile.

Not all of the leftist parties supported the Mojahedin's call to arms. Significantly, both the Tudeh and the Fadayan Majority condemned the insurrection and proclaimed their loyalty to the constitutional process. Even though these parties were permitted to function within narrowly circumscribed limits, the IRP leaders remained deeply suspicious of them. Both parties were distrusted because of their espousal of Marxist ideas. In addition, a widespread perception prevailed that the Tudeh was subservient to the Soviet Union, an attitude derived from the Tudeh's historic practice of basing its own foreign policy stances upon the line of the Soviet Union. In the autumn of 1982, toleration for the Tudeh dissipated quickly once the party began to criticize the decision to take the Iran-Iraq War into Iraqi territory. In February 1983, the government simultaneously arrested thirty top leaders of the Tudeh and accused them of treason. The party was outlawed, its offices closed, and members rounded up. Subsequently, Tudeh leaders were presented on television, where they confessed to being spies for the Soviet Union.

After the spring of 1983, the only nonreligious political party that continued to operate with legal sanction was the IFM. Prominent members included the former prime minister, Bazargan, and the former foreign minister, Ibrahim Yazdi, both of whom were elected to the first Majlis in 1980. The IFM opposed most of the policies of the IRP. Whenever Bazargan or another IFM member dared to speak out against IRP excesses, however, gangs of hezbollahis ransacked party offices. Bazargan was subjected to verbal abuse and even physical assault. He was powerless to protect one of his closest associates from being tried and convicted of treason for actions performed as an aide in the provisional government. Although Bazargan was reelected to the Majlis in 1984, he was barred from being a candidate in the 1985 presidential elections. In practice, the IFM has been intimidated into silence, and thus its role as a loyal opposition party has been largely symbolic.

The IRP's success in silencing or eliminating organized opposition was directed not only at political parties but also was extended to other independent organizations. Even religious associations were not exempt from being forcibly disbanded if they advocated policies that conflicted with IRP goals. Although it emerged as the dominant political party, the IRP leadership failed to institutionalize procedures for developing the IRP into a genuine mass party. IRP offices were set up throughout the country, but in practice these did not function to recruit members. Rather, the offices served as headquarters for local clergy who performed a variety of political roles distinct from purely party functions. At both the national and the local levels, the IRP's clerical leaders perceived themselves as responsible for enforcing uniform Islamic behavior and thought. Thus, they generally viewed the party as a means of achieving this goal and not as a means of articulating the political views of the masses. In actuality, therefore, the IRP remained essentially an elitist party.

The debate within the political elite on power distribution and economic policy also adversely affected the IRP. Intensified dissent over economic programs, beginning in 1986, virtually paralyzed the party. Consequently, President Khamenehi, who had become the IRP's secretary general in 1981 following the death of Beheshti and several other key party leaders, decided it would be politically expedient to disband the IRP. Khamenehi and Rafsanjani jointly signed a letter to Khomeini in June 1987, in which they notified him of the party's polarization and requested his consent to dissolve the party. The faqih agreed, and the political party that had played such an important role during the first eight years of the Republic ceased to exist.

Data as of December 1987