After the revolution, Ahmadinejad was a founder member of a militant student group called "Strengthen the Unity", which was dedicated to upholding the deeply conservative Islamic agenda of Khomeini's revolution, including the return of Sharia. It was this group that, later in 1979, was responsible for occupying the American embassy and holding the 52 staff hostage for more than a year. After Ahmadinejad became president, five former American hostages surfaced to claim that he had been involved in the embassy takeover, although a comprehensive investigation conducted by the CIA was unable to verify their claim. He was, though, one of the central players in the group of student activists responsible for taking over the embassy, a fact that has since been confirmed by senior Iranian government officials who said he worked as a liaison officer between the student occupiers and Khomeini's office.

For the poor peasant boy born in the desert town of Aradan in 1956, the experience had a profound effect. In his lowly capacity as the students' liaison officer, Ahmadinejad was nevertheless able to meet Khomeini several times. The ayatollah made a deep and lasting impression on the young Islamic activist. Like many young revolutionaries, Ahmadinejad regarded Khomeini as his political mentor as well as his religious leader. Ahmadinejad's active involvement in student politics also meant that he met many of the other key figures in the Islamic revolution, notably Ali Khamenei, who succeeded Khomeini as the country's supreme leader after his death, and the future president Ali Akbar Rafsanjani, whom Khomeini had nominated as his interlocutors with the students.

Ahmadinejad's political development also owes much to his experience as a founder member of the Revolutionary Guards, which were established by Khomeini shortly after his return from exile to safeguard the purity of his Islamic revolution. Khomeini believed this was essential to protect the revolution from the competing ideologies of Iranian communists, socialists and nationalists who were attempting to seize control of the revolution for their own ends following the Shah's ignominious departure into exile. Ahmadinejad enthusiastically supported Khomeini's more militant Islamic ideology, and quickly acquired a reputation as a conservative hardliner who was prominent in championing the virtues of the revolution. He explained that it was vital for Islamists "to defend the totality of the new regime and respond to its needs".