The mechanical creep and recovery behavior for uniaxial loading of a short glass-fiber reinforced polyester composite, SMC-R50, with random fiber orientation was investigated experimentally and theoretically. The strain at different stress levels and temperatures was measured during isothermal tests involving several loading-unloading cycles; each cycle consisted of a period of constant load and zero load. Repeatable creep and recovery response was observed only after several cycles; an accelerated mechanical conditioning method was used, in which the duration of each cycle was progressively increased. It is shown that the thermally complex, linear viscoelastic response of SMC-R50 in the mechanically conditioned state can be described by the time-dependent and temperature-dependent behavior of the matrix system and micromechanics calculations of the effective properties of the composite. The data analysis methods for parameters of the model are discussed and illustrated. Master curves for the matrix and for the in situ matrix, the matrix in the composite, were obtained and found to be virtually the same. In order to achieve this agreement it was necessary to use a micromechanics analysis in which the reinforcement is properly modeled as viscoelastic, orthotropic ribbons rather than isotropic, elastic fibers.