We developed a technique based on the use of microsensors to measure pH and H₂ gradients during microbial electrosynthesis. The use of 3D electrodes in (bio)electrochemical systems likely results in the occurrence of gradients from the bulk conditions into the electrode. Since these gradients, e.g., with respect to pH and reactant/product concentrations determine the performance of the electrode, it is essential to be able to accurately measure them. Apart from these parameters, also local oxidation-reduction potential and electric field potential were determined in the electrolyte and throughout the 3D porous electrodes. Key was the realization that the presence of an electric field disturbed the measurements obtained by the potentiometric type of microsensor. To overcome the interference on the pH measure, a method was validated where the signal was corrected for the local electric field measured with the electric potential microsensor. The developed method provides a useful tool for studies about electrode design, reactor engineering, measuring gradients in electroactive biofilms, and flow dynamics in and around 3D porous electrodes of (bio)electrochemical systems.