Composite Sandwich Panels (CSP) are a novel type of wall panels, which has gained immense attraction in the construction industry due to its better mechanical performance with lighter weight. Finite Element Model (FEM) was developed to determine the fire performance of CSP under standard and hydrocarbon fire conditions. Developed FE model was verified with the experimental results of the previous studies. Thirty-six (36) parametric studies were conducted to determine the fire performance of CSP wall panels of different thicknesses with Autoclaved Aerated Concrete (AAC) and Foamed Concrete (FC) under standard and hydrocarbon fire conditions. The FE results showed that composite sandwich panels with AAC core has improved 9%–92% insulation fire rating compared to AAC PCP for different thicknesses. At the same time, FC CSP displayed a reduction in insulation fire rating compared to FC PCP. Moreover, it could be observed that FC of density 1000 kg/m3 CSP has shown the best insulation fire performance under both fire conditions. AAC CSP has shown better performance than the 650 kg/m3 density FC CSP. Comparing Plain concrete panels, FC 650 kg/m3 density has shown the best insulation fire performance, followed by FC 1000 kg/m3 density and AAC. Therefore both materials could be utilised as composite sandwich panels with better thermal performance and mechanical performance.