Upon hearing of the defeat in Nihawānd, Yazdegerd along with Farrukhzad and some of the Persian nobles fled further inland to the eastern province of Khorasan. Yazdegerd was assassinated by a miller in Merv in late 651. His sons, Peroz and Bahram, fled to Tang China. Some of the nobles settled in Central Asia, where they contributed greatly to spreading the Persian culture and language in those regions and to the establishment of the first native Iranian Islamic dynasty, the Samanid dynasty, which sought to revive Sassanid traditions.

The abrupt fall of the Sassanid Empire was completed in a period of just five years, and most of its territory was absorbed into the Islamic caliphate; however, many Iranian cities resisted and fought against the invaders several times. Islamic caliphates repeatedly suppressed revolts in cities such as Rey, Isfahan, and Hamadan. The local population was initially under little pressure to convert to Islam, remaining as dhimmi subjects of the Muslim state and paying a jizya. In addition, the old Sassanid "land tax" (known in Arabic as Kharaj) was also adopted. Caliph Umar is said to have occasionally set up a commission to survey the taxes, to judge if they were more than the land could bear.