Pahlavi has repeatedly called for intervention by US President Donald Trump, who has not acted despite several warnings to Tehran.
The son of Iran's late shah said Friday he is confident the Islamic Republic will fall amid mass protests and called for international intervention.
"The Islamic Republic will fall — not if, but when," Reza Pahlavi told a news conference in Washington. "I will return to Iran."
Pahlavi has lived in exile in the United States since the 1979 Islamic revolution toppled his pro-Western father.
Many protesters have chanted Pahlavi's name in mass protests that swept Iran, which the regime in Tehran violently suppressed. At least 2,572 people have been killed in the crackdown, according to human rights organisations, although some sources claim the toll could reach 15,000.
Pahlavi said he wants to serve as a figurehead to lead a transition to a secular democracy, despite detractors.
Pahlavi has repeatedly called for intervention by US President Donald Trump, who has not acted despite several warnings to Tehran.
"Iranian people are taking decisive actions on the ground. It is now time for the international community to join them fully," Pahlavi said.
He called on the international community to "protect the Iranian people by degrading the regime's repressive capacity, including targeting the Islamic Revolutionary Guard leadership and its command and control infrastructure."
He also called on all countries to expel Islamic Republic diplomats.
Pahlavi issued a call for protests on 8 January, which the Iranian government has since used as a legal turning point.
Iran's justice minister said this week that mere presence on streets after that date is now considered a criminal act, arguing the situation transitioned from "protest" to "internal conflict".
Trump said Wednesday he has been told by "good authority" that plans for executions in Iran have stopped, although Tehran has indicated fast trials and executions ahead in its crackdown on protesters.