Void growth and failure in an epoxy resin is investigated. Tensile tests are carried out on double-notched round bars. Stress triaxiality in the net section is controlled by the use of two different notch root radii. SEM and computed tomography observations are conducted on regions of interest to identify voids and evaluate their growth. Failure initiation sites are analysed, revealing critical defects in the form of voids or particles. The macroscopic and microscopic experimental results are used to optimize the Gurson–Tvergaard–Needleman model. A finite element analysis is performed to study the mechanical response of the notched specimens. The peaks of the maximum principal stress are found to coincide with the locations of the failure initiation sites observed experimentally, and the model is shown to be able to handle non-uniform initial void distributions.