The aim of this study was to assess the physical phenomena that influence the rheological behaviour of polylactide/organo-modified clay nanocomposites. A model was proposed to explain the decrease in non-linear viscosity at high clay contents. Several variables were studied, including shear rate, temperature, clay volume fraction, and polymer molar mass. When the effects of the molar mass and temperature were separated from that of the clay volume fraction, the results suggested a decrease in viscosity compared with that of neat polylactide, which was mostly assigned to molar mass degradation and partially assigned to enhanced temperature dependency. The time-temperature superposition principle was employed for this purpose and highlighted two distinct trends in the activation energies with the clay volume fraction. Ultimately, rheological measurements were corroborated by morphological observations to reveal a non-monotonic evolution of viscosity with the clay volume fraction. These results help provide insight into simulation of the flow behaviour of a nanocomposite based on layered silicate.