The existence of Brønsted-Evans-Polanyi (BEP) relationships, which relate elementary reaction barriers to reaction thermodynamics across a space of different catalysts, has been extensively investigated for reactions on traditional heterogeneous catalysts, and BEP’s are known to provide the central physical paradigm underlying the existence of volcano plots and other trends-based descriptions of catalytic reactivity. However, the extension of such relationships to elementary electrochemical reactions, simultaneously spanning a space of both different applied voltages and different catalyst surfaces, has been widely discussed but never verified. In this contribution, the BEP model is explicitly shown to describe both multiple catalyst surfaces and variable voltages in electrochemical environments. For proton-coupled electron transfer to surface nitrogen (N*) and nitric oxide (NO*), reaction energies and activation barriers are calculated using density functional theory on a parallel plate capacitor model at three different potentials and for nine different transition metal surfaces. Linear BEP relations that describe all potentials and catalyst surfaces are obtained for these elementary reactions, and the slopes of the correlations are shown to be directly related to the fractional coordinate of the transition states (FCTS) of the reactions. The results, which are explained in terms of Marcus Theory, prove a direct equivalence between unified BEP coefficients, describing both variable catalyst surfaces and voltages, and electrochemical symmetry factors and provide a straightforward means of estimating this quantify for proton-coupled electron transfer reactions on transition metal surfaces. The resulting relationships, in turn, could lead to predictions of electrocatalytic reactivity trends of enhanced accuracy and efficiency.