Traditional understanding of electrocatalytic reactions has primarily focused on the covalent interactions between adsorbates and catalyst surfaces, often overlooking the significant influence of the electrolyte on the catalytic process. Recently, researchers have highlighted the pivotal role of cations in the electrolyte, demonstrating their capability to modulate the reaction pathways and thus the activity and selectivity. These findings underscore the need for a deeper, atomic-level understanding of the electrode–electrolyte interface. This perspective presents the mechanisms through which cations affect electrocatalysis, with a focus on the hydrogen-bond network, the adsorption behavior of reaction intermediates, the electric field within the electrochemical double layer, and the local electronic properties of catalysts. It provides a summary of the influences of cations on various electrocatalytic reactions, including hydrogen oxidation reaction (HOR), hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), nitrogen reduction reaction (NRR), nitrate reduction reaction (NO₃⁻RR), and carbon dioxide reduction reaction (CO₂RR). At the end, future research directions are provided to maximize the potential of leveraging the cation effects in the design of more efficient electrolyte systems.