Information Minister Charles Rizq said after a weekly cabinet meeting on Thursday that public prosecutor Adnan Addum will be replaced by Judge Said Mirza.
General Ashraf Rifi would replace General Ali Haj at the head of the Internal Security Forces, while General George Khury replaces General Raymond Azar as head of army intelligence.
Rizq said General Edward Mansur, head of State Security, was removed from office and would be replaced at a future cabinet session.
The dismissals come a few days after the resignation of General Security Chief Jamil al-Sayyid who said he was stepping down to avoid confusion, and because of a change in policy dictated by changing political developments.
General Ali Haj too had offered to step down temporarily until the completion of investigation into the killing of al-Hariri.
Al-Sayyid and Haj were among several security leaders whose removal has been demanded by the opposition for suspected direct or indirect involvement in the killing.
After assuming office, Prime Minister Najib Miqati had said his government was committed to meeting demands for the firing of security chiefs.