2D lamellar materials can offer high surface area and abundant reactive sites, thus showing an appealing prospect in photocatalytic hydrogen evolution. However, it is still difficult to build cost‐efficient photocatalytic hydrogen evolution systems based on 2D materials. Herein, an in situ growth method is employed to build 2D/2D heterojunctions, with which 2D Ni‐based metal–organic layers (Ni‐MOLs) are closely grown on 2D porous CdS (P‐CdS) nanosheets, affording traditional P‐CdS/Ni‐MOL heterojunction materials. Impressively, the optimized P‐CdS/Ni‐MOL catalyst exhibits superior photocatalytic hydrogen evolution performance, with an H2 yield of 29.81 mmol g−1 h−1. This value is 7 and 2981 times higher than that of P‐CdS and Ni‐MOLs, respectively, and comparable to those of reported state of the art catalysts. Photocatalytic mechanism studies reveal that the enhanced photocatalytic performance can be attributed to the 2D/2D intimate interface between P‐CdS and Ni‐MOLs, which facilitates the fast charge carriers’ separation and transfer. This work provides a strategy to develop 2D MOL‐based photocatalysts for sustainable energy conversion. The ultrathin structure and large specific surface area of the P‐CdS/Ni‐MOL composites are of great benefit for exposing more active sites and expanding contact surface area. In such a way, the recombination of photoinduced electrons/holes pairs can be efficiently inhibited. The synergistic effect of the intimate contact between P‐CdS and Ni‐MOLs can significantly enhance the photocatalytic H2 evolution performances.