Mir Qasim was the Nawab of Bengal from the year 1760 till 1764. The British East India Company made him the Bengal Nawab by replacing Mir Jafar, the father-in-law of Mir Qasim, who was also installed by the British in reply to his treachery in the Battle of Palashi. Since Mir Jafar engaged himself with the Dutch East India Company to assert independence, the British finally defeating Mir Jafar and the Dutch forces at Chinsura and made Mir Qasim the new Nawab of Bengal.

After becoming the Nawab of Bengal, Mir Qasim was subject to pay a huge outstanding debt of the former Nawab, Mir Jafar who was also made the Nawab of Bengal by the British as a result of his treachery in the Battle of Plassey. In the pursuit of pleasing the British, Mir Qasim robbed all, seized lands, reduced the purse of Mir Jafar and depleted the treasury. He also transferred the districts of Midnapur, Burdwan and Chittagong to the British East India Company. He thought that since he had given the Company so much, he should therefore be offered the complete authority to rule West Bengal. Thus, he undertook several strategic measures in administration in order to be equipped with a regimented force and ample of funds. In the process he changed his capital from Murshidabad to Munger and also reformed the land revenue structure to raise the revenue.

The small crusade of Mir Qasim against the British was significant and was regarded as the direct fight against and outsider by a native Bengali. Dissimilar to Siraj-ud-Daulah, Mir Qasim was a very popular and effective ruler. The defeat of Mir Qasim in the hands of the British in the Battle of Buxar made the British as the conquerors of. Defeated by the English, Qasim fled to Oudh. He had a sharp diplomatic sense and was able to get the support of the wandering emperor Shah Alam II and Shuja-Ud-Dulla of Oudh. But the combined forces were defeated by the British in the Battle of Buxar. After that, Mir Qasim became underground until his death in Delhi probably in the year 1777.