Later in his life, he joined the National University of Sciences and Technology (NUST) as a visiting professor of theoretical physics.

[4][6] By the time he published his thesis in 1953, he received a Gold medal from the Punjab University for post-graduate contributions to physics and mathematics.

[5] Riazuddin's dissertation was written on "Charge Radius of Pion" which also covered many issues relevant to the field of quantum theory.

[7] Riazuddin left the United States for Italy as he was asked by Salam to join the International Centre for Theoretical Physics in 1970.

In 1959, Riazuddin was the first physicist to use the dispersion relation for Compton scattering of virtual photons on pions to analyse their charge radius.

He seldom published papers, preferring long correspondences with his brother Fayyazuddin, mentor Abdus Salam, and colleagues including Asghar Qadir, Michael Duff, and Masud Ahmad.

[12] In 1965, Riazuddin carried out the pioneering work on vector currents, in which he showed the discrepancy between μ-decay and the constant gravity, and the strong interaction renormalisation of the Beta (β)-decay.

After the introduction, the symmetries break the Standard Model of particle physics, even when the contribution from penguin diagrams is included.

In 1972, Riazuddin and Fayyazuddin were the first to post mathematical frameworks of Current-algebra in neutrino scattering to determine the Scale invariance of Chiral symmetry breaking the Hamiltonian Quantum Mechanics.

In 2008, Riazuddin pointed out that the neutrino mass has μ and τ symmetry and the Lepton number remains constant, a new type of Seesaw mechanism is formed, the so-called Riazuddin's Seesaw Model, the Dirac mass matrix provided the Yukawa coupling to follow the Majorana fermion to satisfy the Leptogenesis asymmetry.

[19] In an experiment performed at the Synchrotron light source installed at the National Center for Physics (NCP), now the Abdus Salam Centre for Physics, Riazuddin observed the decay of the Tau particle, in which he theorised that hadronisation vector currents and axial vectors can be used to study the implicit properties and functions of hadronic resonances, together with Chiral symmetry.

[19] During his stay at PAEC, Riazuddin and Fayyazuddin were central figures of Pakistan's atomic program during the early and critical years.

[20] Salam asked Riazuddin to report to Munir Ahmad Khan – chairman of the Pakistan Atomic Energy Commission at that time.

[22] The Theoretical Physics Group took research in fast neutron calculations – how neutrons moved in a nuclear chain reaction – the theory simultaneity — how would fission weapon would detonated from several points at the same point during the detonation process – and hydrodynamics – how the explosion produced by a chain reaction might behave – and what kind of and how much fissile material and reflectors would be used.

Riazuddin was among the scientists who attended the Multan meeting that was managed by Salam and convened by Pakistan President Zulfikar Ali Bhutto.

[24] Although Salam had traveled to the United States to evade the Indo-Pakistani war of 1971, he returned to Pakistan with stacks of historical books on the Manhattan Project in December 1971.

[26] There, he became a senior research scientist at the University of Maryland, and obtained the open-source information on the "Manhattan Project" from the Library of Congress.

[27] Riazuddin carefully studied American theoretical physicist J. Robert Oppenheimer's approach to develop the first implosion device, and made further advances on Tolman–Oppenheimer–Volkoff limit, Oppenheimer–Phillips process, Born–Oppenheimer approximation.

After his return from the United States, Riazuddin was inducted into the Pakistan Atomic Energy Commission (PAEC) as member (technical).

Shortly after the India surprise nuclear test — Pokhran-I, Munir Ahmad Khan called for a meeting to initiate the work on atomic bomb.

[31] Riazuddin and Salam represented the Theoretical Physics Group (TPG), and it was decided to develop the implosion method for the first device.

He was most famous for his TPG Group work Riazuddin and his team of theoretical physicists are widely credited to have developed and designed Pakistan's nuclear weapon devices.

On 26 April 2009, a day-long conference was held in Islamabad to pay tribute to an eminent research scientist and theoretical physicist, Riazuddin.

In the conference, Masud Ahmad, who is also the student of his, said: "Prof. Riaz always put in his best efforts to obtain original results while working on various issues related to science and technology".