Saeed bin Abdullah al-Qahtani was promoted to the rank of general and named head of public security in decrees issued, respectively, by King Fahd and Interior Minister Prince Nayef bin Abdul Aziz, the official SPA news agency reported.
He succeeds General Asaad bin Abdul Karim al-Fraih, who was named advisor to Prince Nayef.
The move comes amid a crackdown by security forces on Islamist rebels following the Riyadh blasts on May 13. Some 128 people have been rounded up in the hunt.
The Imam of Mecca's Grand Mosque meanwhile deplored in his Friday sermon the fact that even the holy cities of Mecca and Medina, where arrests have also been made, were being used as sites for armed activities.
Urging parents to shield their sons from "intellectual deviation", Imam Sheikh Abdul Rahman bin Abdul Aziz al-Sudais said a minority of youths had engaged in "extremism, violence and terrorism", becoming a "poison" in society.
"Criminality has peaked with the booby-trapping of holy books (Koran) and the use of mosques for armed activity. What makes it worse is that terror and atheism are being practiced in the shadow of the two holiest shrines" in Mecca and Medina, the Imam said.
Sudais said youth should be taught the provisions of Islamic law, such as "the prohibition on killing oneself" or attacking non-Muslims living in Islamic countries.
They should also be taught not to "indiscriminately hurl the label of atheism and not to confuse between legitimate jihad (holy struggle or war) and ... the terrorizing of peaceable people", he said.
Those who destabilize their society should be punished under Islamic law in order to protect the community, he said.