The use of electrochemistry to form C–N bonds in small molecules represents a more sustainable production method than traditional reactors, which require high heat and pressure. However, one of the primary limitations of electrochemical methods for C–N bond production is poor Faradaic efficiency due to nonselective catalysts and water electrolysis reactions. Herein, we use the oxidation of methanol in the presence ammonia, a useful model system employing small molecules that can be derivatized, to demonstrate how an externally applied magnetic field can improve Faradaic efficiency for C–N bond-containing products, namely promoting the generation of formamide over formate. Through Lorentz-force-induced magnetohydrodynamics, product ratios are altered with no additional chemical or energy input as convection is generated at the electrode surface by a permanent magnet that is outside the reactor. This approach promotes mass-transport-dependent products externally, permitting its employment in reactors with novel geometry, low volume-to-surface-area ratios, or other configurations in which traditionally applied convection (mechanical stirring) is ineffective or impossible. As novel reactor designs become more important for scaling electro-organic synthesis, permanent magnets represent a method for tuning reactions in spaces inaccessible to traditional stirrers. Furthermore, the improvement resulting from mass transport suggests generalizability to other electro-organic syntheses beyond the methanol-ammonia system