Chromium tetraphosphide (CrP₄) nanopowder was synthesized via high-energy mechanical milling (HEMM) and introduced as an anode for lithium ion batteries (LIBs) and sodium ion batteries (SIBs). The as-synthesized monoclinic CrP₄ nanopowder was slightly agglomerated nanoparticles of 100–200 nm consisting of 10–20 nm-sized nanocrystallite aggregates. The CrP₄ electrode underwent conversion reactions with both Li and Na ions by forming Li₃P and Cr for LIBs and Na₃P and Cr for SIBs and exhibited high initial discharge and charge capacities (1776 and 1540 mA h g⁻¹ for LIBs and 1125 and 881 mA h g⁻¹ for SIBs, respectively), implying its potential as a high energy density anode for both LIBs and SIBs. In addition, the CrP₄/carbon (C) nanocomposite was fabricated by mixing the as-synthesized CrP₄ nanoparticles and acetylene carbon black to improve the long term cyclability and high rate capability of CrP₄. The CrP₄/C nanocomposite electrode delivered a specific capacity of 860 mA h g⁻¹ after 100 cycles at a current density of 1000 mA g⁻¹ in LIBs and 369 mA h g⁻¹ after 100 cycles at 500 mA g⁻¹ in SIBs. In particular, the CrP₄/C electrode showed outstanding high rate capability compared to other transition metal-based phosphide anodes for LIBs. Furthermore, the CrP₄/C electrode showed stable cycling performance even in full cell configuration.