The active damping control strategy upgraded by a multi-objective particle swarm optimization algorithm is utilized for improved broadband suppression of sound transmission through a simply supported piezo-laminated rectangular panel of arbitrary thickness featuring an orthotropic functionally graded viscoelastic material interlayer. The controller parameters are tuned optimally through multi-objective particle swarm optimization which yields the Pareto optimal frontiers of certain applicable conflicting objective functions. Extensive numerical simulations include the calculated sound transmission loss of the passive, active, and hybrid (active–passive) piezo-composite panels under normally or obliquely incident plane waves. It is found that the overall sound transmission loss levels substantially rise with increasing thickness of (carbon fiber–reinforced) viscoelastic interlayer, which can further be improved by augmenting the fiber volume fraction. Also, the purely active multi-objective particle swarm optimization–based control system performs well in the low-frequency region, while the good performance of the hybrid smart panel is achieved by balancing an optimal trade-off between the active and passive control configurations in a relatively wide frequency range. Accuracy of formulation is confirmed by comparisons with the existing data as well as with those of a finite element model software package. Furthermore, a frequency-domain subspace identification scheme is applied to estimate the state matrices of proposed control systems, and the closed-loop stability is established based on eigenvalue analysis of identified systems.