A progressive lay-up and in-situ cure process is presented for manufacturing thick polymeric composite structures. Manufacturing cycle times can be reduced significantly, since this process combines the lay-up and curing. Also, the material degradation due to thermal spiking which is generally very large in thick-section composites can be avoided, depending on the judicious selection of process variables such as cure temperature, ambient temperatures, and material supply rate. A one-dimensional combined thermo-chemical heat transfer model was developed and solved numerically in order to monitor the cure, temperature distributions, and thermal spiking through the thickness. In order to validate the analysis, 12 mm thick graphite/epoxy (AS4/3501-6) plates were manufactured by the current process and were scanned by DSC (Differential Scanning Calorimeter). The predicted temperature and degree of cure profiles are compared with experiments. Both results are in good agreement which confirms the accuracy of this cure simulation study. Both graphite/epoxy and glass/polyester systems are investigated in the present paper.