The Gemini Infrared Multi-Object Spectrograph (GIRMOS) is a new facility instrument being designed in close partnership with the upcoming facility adaptive optics (AO) system at Gemini-North observatory called GNAO. GIRMOS will take advantage of both ground-layer and laser tomographic AO offered by GNAO to carry out high angular resolution (0.83-2.4µm) imaging and multi-object integral field infrared (0.95-2.35µm) spectroscopy within GNAO's two arcminute field-of-regard. We present the final design of GIRMOS, which consists of five optical instruments, an imager and four identical deployable integral field spectrographs. This allows for simultaneous imaging over a 85 × 85” field and high-angular-resolution integral field spectroscopy of four objects over the full 2' diameter field-of-regard. The instrument has a second stage multi-object AO (MOAO) system that works in concert with GNAO, providing high angular resolution correction for each spectrograph. The spectrographs offer three spatial sampling scales (0.025, 0.05, 0.1”/spaxel), which correspond to three fields of view (1 × 1”, 2 × 2”, 4 × 4”), and two different spectral resolving power modes (R∼3,000 and 8,000). The spectrographs can be deployed anywhere across the field-of-regard or be packed closely together to observe a single object. The imager offers diffraction-limited imaging in H and K-bands across its full field. Several cardinal science cases have been developed that define the scientific capabilities of the instrument. These include measuring the star formation and kinematic properties of high redshift galaxies, searching for intermediate mass black holes in centers of Milky Way globular clusters, and characterizing the properties of optical/infrared transients. GNAO+GIRMOS offer a unique set of capabilities not currently available in other existing large AO-fed telescopes, enabling highly multiplexed spectroscopic and rapid response/queue scheduled AO observations. The instrument will be entering the construction phase in 2025 with an expected delivery by 2028, the anticipated first light for GNAO. GIRMOS is a pathfinder for future extremely large telescope instrumentation that requires high angular resolution, highly multiplexed spectroscopy.