Metal-organic framework (MOF) layers were grown in situ from 2D transition metal carbides (MXenes, Ti3C2Tx) at room temperature to obtain the two-dimensional (2D) Ti3C2Tx@MOF heterostructures with a tightly connected interface. This interface provided more titanium atoms in the low-valence state in comparison to the original Ti3C2Tx, thus facilitating more electron transfer from Ti3C2Tx to MOF-(Fe/Co) nanosheets. The charge density difference and density functional theory results disclosed that Ti3C2Tx could modulate the electronic density around the active sites and lower ΔGH* energy barrier of 2D MOF-(Fe/Co) nanosheets towards the improved hydrogen evolution reaction (HER) activity. The obtained 2D Ti3C2Tx@MOF heterostructures exhibited a much higher HER activity in 1 M KOH electrolyte (with the overpotential of 104 mV at 10 mA/cm2 and Tafel slope of 79 mV/dec) than those of 2D Ti3C2Tx@MOF-TH, 2D MOF nanosheets, and Ti3C2Tx nanosheets. This research provides a basis for developing superior 2D MOFs, which can enhance HER properties through efficient electronic transport at the heterojunction interface.