Efficient and low-cost transition-metal (TM)-based electrocatalysts have been of great importance for producing hydrogen (H2) and oxygen (O2) via electrocatalytic water (H2O) splitting to ameliorate global energy and environmental problems. However, TM-based materials generally suffer from unsatisfactory electrocatalytic activity because of their relatively low conductivity and unregulated electronic structure. Therefore, the electronic structure engineering of electrocatalysts is an efficient strategic approach to enhance catalytic performances and stabilities. In this review, recent experimental and theoretical advances in the intrinsic electronic structure regulation of TM-based nanomaterials are summarized in terms of preparation methods and underlying natures to boost hydrogen evolution reaction and oxygen evolution reaction. A systematic discussion is conducted on engineering strategies for TM-based nanomaterials to regulate their electronic structures, optimize their adsorption ability of reaction intermediates, and reduce reaction barrier. The existing challenges and perspectives of TM-based electrocatalysts are highlighted to provide new insights into technological advancement for hydrogen production.