Abstract Background Stroke is a leading cause of long-term disability worldwide. Neuromuscular electrical stimulation (NMES), such as the geko™ device, may enhance cerebral perfusion post-stroke by improving venous return. This study evaluated the cortical haemodynamic effects of NMES in subacute stroke survivors using functional near-infrared spectroscopy (fNIRS). Methods A prospective observational study was conducted in 18 patients (>7 days post-ischaemic stroke) receiving bilateral lower limb NMES. fNIRS measured changes in oxyhaemoglobin (HbO) and deoxyhaemoglobin (HbR) concentrations across varying NMES intensities and postures (supine, semi-supine, and upright). Data were analysed using a general linear model, with β-values reflecting haemodynamic response magnitude. Results NMES evoked significant cortical haemodynamic responses, with increased HbO observed across multiple sensorimotor regions. Upright posture significantly enhanced cortical tissue oxygenation (p=0.010). Higher stimulation intensities produced greater HbO responses, indicating a dose-dependent effect. Larger infarct size (>5 cm) was associated with increased haemodynamic response. These findings suggest NMES may influence neurovascular coupling and cerebral autoregulation during stroke recovery. Conclusions NMES via the geko™ device enhances cortical oxygenation in subacute stroke, particularly in upright positions and at higher intensities. The results support the potential use of NMES not only for venous thromboembolism prevention but also as an adjunctive strategy to promote cerebral perfusion and facilitate rehabilitation. Further trials are warranted to explore clinical efficacy and functional outcomes.