Hydrogen embrittlement is the phenomenon by which metallic materials experience a drastic decrease in their mechanical properties, such as ductility and fracture toughness, when exposed to hydrogen, with properties being reported to degrade by an order of magnitude or more. This remarkable degradation of metals when exposed to hydrogen is currently one of the biggest obstacles holding back the full implementation of hydrogen as a net-zero fuel to decarbonise a wide range of industries. Most of the existing research on hydrogen embrittlement is based on experimental results, and different mechanisms have been proposed, although they are mostly restricted to some specific materials and loading conditions. However, a good understanding is still missing, which makes it extremely difficult to generalise for different materials and predict the impact of hydrogen beyond the range of the experimental results. This is why in this paper we aim to provide a deeper understanding of the effects of hydrogen on the behaviour of the different metals by developing a completely new framework that combines crystal plasticity, hydrogen diffusion and hydrogen embrittlement based fully on mesoscale first principles, which can be used in any general finite element software like Abaqus. The numerical implementation of this new framework is based on a novel phase-field-like approach with which we are able to explicitly account for the microstructure of the material, being able to capture local phenomena like hydrogen segregation and localised embrittlement, all within the framework of finite elements. Successful results have been obtained for capturing some phenomena that until now remained obscure, like grain boundary segregation or some of the a priori contradictory effects of hydrogen in metals.