Different experimental techniques (X-ray diffraction, neutron diffraction with isotopic substitution, extended X-ray absorption spectroscopy) and theoretical methods (reverse Monte-Carlo simulation, molecular dynamics modelling, Voronoi analysis) were applied to elucidate the atomic structure of Ni–Zr and Cu–Zr alloys in glassy and crystalline states and to explain differences in the glass-forming abilities of the Ni64Zr36 and Cu65Zr35 compositions. Both glasses show similar strong topological ordering, but it is established that the degree of chemical ordering is much more pronounced in Ni64Zr36 glass than in Cu65Zr35 glass. The short-range atomic order and topology in the glassy and crystalline structures are remarkably different, and these differences are presumed to hinder crystal nucleation and growth, hence promoting glass formation upon fast cooling of the Ni64Zr36 and Cu65Zr35 liquid alloys. The larger differences observed for the Cu65Zr35 alloy in glassy and crystalline states are suggested to play a decisive role in increasing its bulk-glass-forming ability.