<p>In this work, the electrochemical deposition process of CuNi alloy nanoparticles on a glassy carbon electrode, from their metal precursors dissolved in a eutectic mixture of choline chloride/urea, was investigated by cyclic voltammetry and chronoamperometry techniques. From voltametric results, CuNi alloy could be electrodeposited in one potential step from the eutectic mixture and the activation energy for ions bulk diffusion of Cu(II)-Ni(II) to form the CuNi alloy requires higher values than its individual components. From chronoamperometry, the electrochemical phase formation of CuNi alloys from the eutectic mixture was explained by a model comprising: adsorption, 3D nucleation and diffusion-controlled growth on bimetallic nuclei contribution, and residual water reduction with the induction time correction, which was validated by surface characterization techniques. The obtained equal molar Cu_0.5Ni_0.5 alloy has presented strong electrocatalytic activities and outstanding corrosion resistance in acidic media (better than their alloying component, glassy carbon, and closer to commercial catalyst Pt/C nanoparticles). The results have shown that the CuNi alloy electrodeposited from the eutectic mixture of choline chloride/urea could be a cost-effective alternative to replace Pt for hydrogen evolution reaction in acidic media.</p>