His career was mostly spent in the Government of Pakistan as a public policy official where he pushed for peaceful and commercial usage of the nuclear energy, and later working on arms control with Ministry of Defense to become a party of Partial Test Ban Treaty in 1963 before joining the International Atomic Energy Agency (IAEA) as its Chair of its Board of Governors.

: 57 [5] Usmani went to the United Kingdom to attend the doctoral program in physics at the Imperial College in London, to work under George Paget Thomson on electron diffraction.

[7] In 1941, Usmani was conferred with PhD in atomic physics, just aged 23, and subsequently returned to India in 1942, where he qualified for the examination for the Indian Civil Service (ICS).

: 15 [2] In 1967, Usmani played a pivotal role in securing the federal funding for establishing the Institute of Nuclear Science and Technology near Islamabad– a visionary national laboratory site functioning under Dr. Abdus Salam, a theoretical physicist.

[10][6] Usmani was well known for his support for the anti-nuclear weapons movement, and saw the American 'Project Plowshare' tests for using nuclear bombs to create artificial lakes as ineffective and insignificant.

Usmani was widely notorious at PAEC for disrupting research on nuclear materials by transferring scientists to non-technical and corporate positions.

: 90 [12] On 20 January 1972, President Zulfikar Ali Bhutto relieved Usmani from the Chairmanship by appointing Munir Ahmad Khan, a reactor physicist, in his place.

: 90 [12]: 11 [13] Usmani was dispatched to the Ministry of Science and Technology as its Secretary, remaining involved with the PAEC's matter,[clarify] and continued lobbying for arms control.

[14] Although, Usmani was notified and knew well that the atomic bomb project was a complete success, the program has gone mature, and the critical phase of producing the fissile cores had been achieved since 1978.

[14] He remained with the IAEA until 1985 when he joined the Bank of Credit and Commerce International (BCCI) to oversee the funding and construction of the University of Computer and Emerging Sciences and the Ghulam Ishaq Khan Institute of Technology.