Two‐dimensional (2D) materials have emerged as prospective candidates for electronics and optoelectronics applications as they can be easily fabricated through liquid exfoliation and used to fabricate various structures by further subsequent processing methods in addition to their extraordinary and unique optoelectronic properties. Herein, the Ti3C2Tx/ZIS heterostructure with nanometer‐thick Ti3C2Tx‐MXene and ZnIn2S4 (ZIS) films is fabricated by successive interfacial assembly of liquid exfoliated 2D MXene and ZnIn2S4 nanoflakes. Benefiting from the superior light‐harvesting capability and low dark current of ZnIn2S4, the limited absorbance, large scattering coefficient, and high dark current disadvantages of MXene are ameliorated. Meanwhile, the separation and transport of photogenerated carriers in ZnIn2S4 are improved due to the excellent electrical conductivity of Ti3C2Tx nanoflakes. As a result, the as‐prepared Ti3C2Tx/ZIS heterostructure photodetector has excellent optoelectronic characteristics in terms of a high responsivity of 1.04 mA W−1, a large specific detectivity up to 1 × 1011 Jones, a huge on/off ratio at around 105, and an ultralow dark current at ≈10−12 A. This work demonstrates a convenient method to construct heterostructured photodetectors by liquid exfoliated 2D nanoflakes, the as‐fabricated Ti3C2Tx/ZIS heterostructured photodetectors show promising application potential for low‐cost, reliable, and high‐performance photodetectors.