A multiscale fracture model for low-permeability brittle rocks which accounts for their microstructure is presented. The work hinges on a microcrack-damage model within a poroelasticity and multiscale framework. A set of damage tensors describes the effect of dual-scale porosities (nanopores and microcracks) on both the hydraulic and poroelasticrock properties. Failure is formulated as a material degradation phenomenon driven by microcrack growth which impacts on hydro-mechanical properties. Essentially, the multiscale model reconstructs the coupling effect of hydro-mechanical forces at the continuum level from the ground up through the upscaling of the phase interactions at the fundamental scales of the material, which is novel in rock mechanics applied to hydraulic fracturing. As an illustration of the enhanced capabilities of the developed model, numerical simulations based on the extended finite element method are presented consideringbench mark problems and lab experimental results of hydraulic fracturing in heterogeneous brittle rocks.