The Deep Underground Neutrino Experiment (DUNE) is a future long-baseline neutrino oscillation experiment featuring a 70 kt liquid argon (LAr) far detector. The near detector complex, situated at Fermilab, includes NDLAr - a LAr detector that is critical for constraining systematic uncertainties via in situ measurements to enable precision studies of neutrino oscillations. Challenging event pile-up from the world's most intense 1.2 MW neutrino beam will be mitigated by a combination of a modularised detector design and state-of-the-art readout technologies. True 3D pixel-based charge readout capabilities combined with high-timing resolution of the light readout will eliminate ambiguities that would otherwise arise in conventional LAr detectors. This document describes the novel design of the detector and its subsystems, highlighting the key performance results from commissioning and the current status of the NDLAr 2x2 Demonstrator, an NDLAr prototype that has recorded the first neutrino data for the DUNE collaboration.