We present an innovative, multiscale computational approach to probe the behaviour of polymer-clay nanocomposites (PCNs). Our modeling recipe is based on 1) quantum/force-field-based atomistic simulation to derive interaction energies among all system components; 2) mapping of these values onto mesoscopic bead-field (MBF) hybrid-method parameters; 3) mesoscopic simulations to determine system density distributions and morphologies (i.e., intercalated versus exfoliated); and 4) simulations at finite-element levels to calculate the relative macroscopic properties. The entire computational procedure has been applied to two well-known PCN systems, namely Nylon 6/Cloisite 20A and Nylon 6/Cloisite 30B, as test materials, and their mechanical properties were predicted in excellent agreement with the available experimental data. Importantly, our methodology is a truly bottom-up approach, and no "learning from experiment" was needed in any step of the entire procedure.