This work reports the development of a new robust electrode composed of carbon nanotubes (CNTs) for redox potentiometry to determine ascorbic acid. The electrode was fabricated via catalytic chemical vapor deposition (CVD) of ethylene on Ag substrate in the presence of H₂ gas at 800 °C. The C₂H₂:H₂ ratio was 75:90 ml/min respectively. The prepared electrode was characterized with SEM, TEM, XRD, XPS, and Raman spectrometry. SEM showed the formation of aligned CNTs. XRD and Raman spectrometry proved the formation of CNTs with a good degree of graphitization and high crystallinity. XPS analysis results showed 80% of SP² C–C with a small presence of carbonyls and carboxylates, indicating the high perfection of the CNTs formed. CNT/Ag electrode was applied, for the first time, to zero-current potentiometry and was successfully used to determine ascorbic acid in both pure form and in pharmaceutical formula. Ascorbic acid concentrations down to 0.5 mmol/L was determined. Sigmoidal potentiometric curves were obtained and the results were comparable to those obtained from Pt electrode. The CNT/Ag electrode attained fast equilibrium and exhibited good sensitivity and reproducibility. The enhanced sensing efficiency is attributed to the rapid heterogeneous electron transfer and high electrode surface area offered by CNTs grown via CVD. Additionally, the CVD method produced CNT/Ag electrode with strong adhesion of the CNTs layer to the substrate compared to other CNT-based electrodes prepared by casting the CNTs or mixing them with Nafion. This in turn improves the performance and durability. Moreover, unlike the Pt electrode, the CNT on the surface of this electrode may easily be functionalized by immobilizing the desired moieties via various types of strategies to suit different selective routine applications.