A new model, which represents a unified description of material thermal degradation and burning under thermally thin (non-dimensional), surface radiant heating (one-dimensional) and upward flame spreading (two-dimensional) conditions, has been developed by coupling the numerical pyrolysis solver ThermaKin2D, whose function is to compute the transient rate of gaseous fuel production of a material in response to external heat transfer, with an empirical flame model that predicts a wall flame's heat feedback profile as a function of material mass loss rate. A previously developed pyrolysis model of poly(methyl methacrylate), which was parameterized using a combination of milligram-scale simultaneous thermal analysis experiments and gram-scale gasification tests, was validated in this study using gasification experiments distinct from those utilized in the parameterization process. A previously developed wall flame model was reformulated to include results of new heat flux measurements from 3 to 20 cm above the base of the flame. Inclusion of these results improved the model's predictive capabilities at ignition and across a larger range of flame sizes. The new unified model was employed to predict vertical burning and upward flame spread on 4 and 17.5 cm tall samples of poly(methyl methacrylate). The model predictions - including time to ignition and initial, peak, and rate of rise of sample mass loss rate - were found to closely match experimental results. The impacts of melt flow effects and uncertainties in the flame model formulation on the unified model predictions were examined and found to be moderate. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.