An Active Vertex Model (AVM) for cell-resolution studies of the mechanics of confluent epithelial tissues consisting of tens of thousands of cells, with a level of detail inaccessible to similar methods is presented. The AVM combines the Vertex Model for confluent epithelial tissues with active matter dynamics. Cell contacts are generated dynamically from positions of cell centres which leads to a natural description of the T1 transition events responsible for local tissue rearrangements. The AVM also includes cell alignment, cell specific mechanical properties, cell growth, division and apoptosis. The AVM introduces a flexible, dynamically changing boundary of the epithelial sheet allowing for studies of phenomena such as the fingering instability or wound healing. We illustrate these capabilities with a number of case studies. An expression for mechanical stress in the model is then derived from the Hardy stress for atomistic simulations. Calculation of stress is important for understanding how cell-level events coordinate to drive morphogenic processes.