The study demonstrates a scalable and reproducible method for synthesising graphene oxide (GO) nanosheets from commercial carbon fibres derived from carbonised polyacrylonitrile (PAN) polymer. An exfoliation route with nitric acid allows for the preparation of monolayer GO nanosheets with a consistent thickness of 0.9 ± 0.2 nm, identical to the commercially available GO from mined graphite. The GO nanosheets exhibit distinct circular and elliptical shapes, in contrast to the polygonal and sharp-edged morphology of commercial GO. An extensive evaluation of acidic solutions and electrical potentials identified a narrow processing window critical for obtaining GO nanosheets sized 0.1–1 µm. An unexpectedly low 5% acid concentration was found to be the most effective, providing a balance between efficient exfoliation through synergistic acidic and electrochemical oxidation. The process provides a high yield of 200 mg of GO per gram of carbon fibre. Advanced characterisation using high-resolution electron and atomic force microscopy (HR-TEM/SEM/AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (FTIR) provided detailed insights into the morphology, thickness, surface functionalisation, and chemical composition of the nanosheets. With its high yield, environmentally sound production, and versatility, the synthesised GO offers transformative potential for large-scale applications, including energy storage, advanced coatings, high-performance composites, water purification, and electronic devices.