Hydrogen embrittlement in structural alloys is governed by the interaction between plastic deformation, microstructural heterogeneity, and hydrogen transport. Continuum modelling of hydrogen diffusion under large deformations has highlighted the importance of coupling between mechanics and transport mechanisms [1]. Building on this, the present work introduces a coupled numerical framework for modelling hydrogen assisted fracture in polycrystalline materials under large deformations, combining crystal plasticity, hydrogen diffusion with reversible trapping, and phase field fracture. Crystal plasticity is used to capture anisotropic slip activity and heterogeneous deformation at the grain scale. Hydrogen transport is formulated in terms of chemical potential gradients and includes Oriani type reversible trapping associated with plastic deformation. Fracture is described using a phase field approach in which the fracture driving force depends on the local hydrogen concentration through a hydrogen dependent fracture energy, following established formulations for hydrogen assisted cracking [2]. The framework is implemented in an Abaqus UMAT and UMATHT environment and applied to polycrystalline specimens with explicitly resolved grain structures. Numerical results show that plastic localisation drives hydrogen accumulation and promotes localised fracture under large deformations.