Exploring efficient nonprecious electrocatalysts for hydrogen evolution reaction (HER) in alkaline media is appealing yet challenging in the field of renewable energies. Herein, we present an experimental and theoretical exploration to demonstrate the in situ formation of binary MXene/Ni3S2 nanosheets over three-dimensional Ni foam (NF) in target functioning as a self-supported and highly effective electrocatalyst for alkaline HER. Benefiting from the outstanding electrical conductivity, superior hydrophilic interface for gas release, and synergistic coupling of Ti3C2Tx and Ni3S2, the HER test on Ti3C2Tx/Ni3S2/NF in 1 M KOH results in a low overpotential (72 mV) to produce a current density of 10 mA cm-2. The Tafel slope in response is 45 mV dec-1, which is among the lowest realized for self-supported Ni-based electrocatalysts as well as the state-of-the-art MXene-involved electrocatalysts in alkaline media. Thus-designed catalyst is highly stable for at least 12 h with no decrease in the current density. Density functional theory calculations further reveal that the hybridization of Ti3C2Tx and Ni3S2 lead to optimized free energy of hydrogen adsorption on the catalyst surface. Our findings might pave a route toward self-supported and cost-effective electrocatalyst design via emerging MXene incorporation for next-generation energy applications.