Abstract Massive Population III stars can die as energetic supernovae that enrich the early Universe with metals and determine the properties of the first galaxies. With masses of about 10⁹ M _⊙ at z ≳ 10, these galaxies are believed to be the ancestors of the Milky Way. This paper investigates the impact of Population III supernova remnants (SNRs) from both Salpeter-like and top-heavy initial mass functions (IMFs) on the formation of first galaxies with high-resolution radiation-hydrodynamical simulations with the ENZO code. Our findings indicate that SNRs from a top-heavy Population III IMF produce more metals, leading to more efficient gas cooling and earlier Population II star formation in the first galaxies. From a few hundred to a few thousand Population II stars can form in the central regions of these galaxies. These stars have metallicities of 10⁻³–10⁻², Z _⊙, greater than those of extremely metal-poor (EMP) stars. Their mass function follows a power-law distribution with dN ( M * ) / dM * ∝ M * α , where M _* is stellar mass, and α = 2.66–5.83 and is steeper for a top-heavy IMF. We thus find that EMP stars were not typical of most primitive galaxies.