During the Second Carnatic War he was a prisoner, first in Nasir Jung's camp and later in Muzaffar Jung's camp. After Muzaffar Jung (his nephew) was killed by the Afghans on 13 February 1751, Mir Sa'id Muhammad Khan was proclaimed as the new Nizam near Lakkireddipalli Pass, by the French under De Bussy with the title "Asaf-ad-Daulah, Nawab Said Muhammad Khan Bahadur, Salabat Jung, Zafar Jung, Nawab Subahdar of the Deccan". He was promoted to the title of "Amir-ul-Mamalik" by the Emperor Alamgir II. He was the ruler of the Hyderabad State in India from 1751 until 1762.