Haidallah became prime minister on 31 May 1979, a few days after the death in an airplane crash of the previous prime minister, Col. Ahmed Ould Bouceif, with whom he had seized power for the CMSN just a month earlier, from Col. Mustafa Ould Salek and the CRMN. In January 1980 he seized power from Ould Salek's successor as head of state, Mohamed Mahmoud Ould Louly. He continued to also hold the position of Prime Minister until December of that year, when a civilian, Sid Ahmed Ould Bneijara, was appointed to the post.