Hydrogen assisted fracture is a coupled problem involving large deformation mechanics, hydrogen transport, and damage evolution. Previous continuum studies have shown that hydrogen diffusion under large deformations must be formulated consistently with the mechanical response of the material. Based on this, we present a numerical framework for modelling hydrogen assisted fracture in polycrystalline materials with explicit representation of microstructural effects. The mechanical response is described using a crystal plasticity formulation, which allows crystallographic orientation effects and plastic strain localisation to be resolved at the grain scale. Hydrogen transport is formulated using a chemical potential based approach and includes reversible trapping associated with plastic deformation. Fracture is modelled using a phase field formulation, following numerical strategies developed for coupled phase field and stress evolution problems, with the fracture driving force depending on the local hydrogen concentration. The framework is implemented in an Abaqus UMAT and UMATHT environment and applied to polycrystalline domains with explicitly resolved grain structures. Numerical simulations show that plastic strain localisation leads to hydrogen accumulation and promotes localised fracture under large deformations. The results highlight the importance of using a unified multiphysics formulation for numerical modelling of hydrogen assisted fracture.