In the recent past, beryllium–boron compounds have been the focus of attention as a consequence of their extremely rich structures and potential applications. Nevertheless, their complex phase structures greatly hinder further exploration of the physical and chemical properties. To this end, we propose a novel beryllium–boron compound based on a two-dimensional (2D) structure, namely a Be₂B₂ monolayer. Using first-principles methods, we first prove that the structure of the 2D Be₂B₂ monolayer is energetically and thermodynamically stable. Subsequently, we systematically explored its potential as a high performance anode material for LIBs and NIBs. The results reveal that the Be₂B₂ monolayer exhibits an excellent, comprehensive performance with a strong adsorption energy, low diffusion barrier, suitable average open circuit voltage and outstanding electronic conductivity. More importantly, the extremely high theoretical specific capacity (1352 mA h g⁻¹ for both LIBs and NIBs) well meets our expectations, which is quite ideal for an anode material. Meanwhile, we hope and believe that this work can provide some new insights into the study of beryllium–boron compounds.