The research work in this thesis is concerned with micromechanical modelling of ductile fracture in API X80 linepipe steel using Gurson-Tvergaard-Needleman (GTN) Model. The modified GTN model is based on simulation of plastic softening and damage behaviour of ductile material based on the introduced approximations for micro-void nucleation, growth and coalescence into its original formulation. The GTN model has been implemented through ABAQUS/Explicit solver which already includes a porous plasticity model based on GTN formulation. A hybrid experimental methodology involving series of interrupted uniaxial tensile tests on smooth and notched round tensile bar specimen of different geometries comprising different stress triaxiality regimes was carried out to estimate the model parameters. Metallographic examinations involving scanning electron microscopy and optical microscopy, and subsequent image analysis using ImageJ, a NIH freeware, and numerical curve fitting approach has been followed for estimating experimentally the initial set of model parameters. The adjustment of experimentally determined model parameters is essential to simulate ductile damage phenomenon considering the constraints imposed by the geometry. A parametric study has thus been conducted to investigate the influence of various model parameters on the material behavior and a calibrated set of model parameters was obtained by comparing experimental and simulated load-diametrical contraction curves for a notched round bar specimen geometry and validated using other notched round bar specimen geometry. The ductile rupture analysis was also carried out to provide a thorough understanding of micromechanics of ductile fracture process in API X80 steel.