After the Western borders had been secured, Gawhar as-Siqilli pushed towards Egypt and occupied the land around the Nile from the Ikhshidids after a siege at Giza. The conquest was prepared by a treaty with the Vizir of the Ikhshidids (by which Sunnis would be guaranteed freedom of religion), so the Fatimids encountered little resistance. Afterwards Gawhar ruled Egypt until 972 as viceroy.
In this capacity he founded the city of Cairo on 969 at Fostat, to serve as the new residence of the Fatimid Caliphs, and the al-Azhar mosque on 970. Although Palestine was occupied after the conquest of Egypt, Syria could not be overcome, following a defeat at the hands of the Carmathians at Damascus. However, when the Carmatians overran Egypt, Gawhar was able to defeat them north of Cairo on the 22 December 970, although the struggle continued until 974. To secure the southern border of Egypt a legation was sent to the Christian land of Nubia.
After the establishment of the residence at Cairo, Gawhar fell into disfavour with al-Muizz. Under his successor al-Aziz (975-996) however, in whose accession to the throne Gawhar played an important role, he was rehabilitated. He was regent again until 979, but was finally stripped of power after a campaign against Syria was once again defeated near Damascus.
Gawhar died on 1 February 992.