Mahmood joined the Pakistan Atomic Energy Commission (PAEC) in 1968, joining the Nuclear Physics Division at the Pakistan Institute of Nuclear Science and Technology (PINSTECH) working under Dr. Naeem Ahmad Khan. His collaboration took place with Samar Mubarakmand, Hafeez Qureshi, and he was a vital member of the group before it was discontinued in 1970. Mahmood was one of the foremost experts on civilian reactor technology and was a senior engineer at the Karachi Nuclear Power Plant (KANUPP I)— the first commercial nuclear power plant in Pakistan. He gained notability and publicity in the Pakistan Physics Society for inventing a scientific instrument, the 'SBM probe', to detect leaks in steam pipes, a problem that was affecting nuclear plants all over the world and is still used worldwide.