In the present research work, the needle-punched nonwoven jute epoxy composites are fabricated by varying the weight percentages of sponge iron slag in vacuum assisted resin transfer molding technique. This study examines the physical, mechanical and thermomechanical properties (i.e., density, water absorption, tensile, flexural, inter-laminar shear strength, compression, impact, fracture toughness and dynamic mechanical analysis) of unfilled and 8 wt.%, 16 wt.% and 24 wt.% of sponge iron slag filled composites under controlled operating conditions. Moreover, it is shown that all the mechanical properties improved with the increased in sponge iron slag content except for tensile strength which increased only upto 16 wt.%. This study also attempted for the analysis of thermal conductivity of the unfilled and particulate filled composites in experimentally by hot disc method. This work also presents both existing empirical models and numerical simulation analysis to evaluate the thermal conductivity of the developed composites. The numerical simulation values of the thermal conductivity demonstrated good agreement with the experimental values. At the end, Cole-Cole plot is drawn between loss modulus and storage modulus to understand the nature of the proposed composites.