He dealt mainly with the Muslim rulers and governments of India, especially with the Mughal and Tughluq dynasties.
He did extensive work on rulers such as Muhammad bin Tughluq, the Sultan of Delhi, Humayun, and Aurangzeb.
His father's untimely death left a very young Ishwari Prasad, a student of class 12th to look after his younger siblings.
During one of his lectures Prof. Rushbrook Williams was present & he believed that Dr. Ishwari Prasad possessed unusual qualifications as a Historian.
He invited him to teach at the University of Allahabad.He was elected Member of Legislative Council from the graduate constituency for 3 terms continuously.