The efficient activation of H2O2 in heterogeneous Fenton-like systems is important for the degradation of organic pollutants. Herein, a Ti3C2 MXene catalyst prepared by a simple HF etching method was used to activate H2O2. Ti3+ self-doped TiO2/Ti3C2 MXene (Ti3+-TiO2/Ti3C2) Schottky heterojunctions were in situ constructed in the photo-Fenton-like system. Owing to the Ti3+-TiO2/Ti3C2 Schottky heterojunctions, abundant multivalence titanium species, and strong surface negative charges, the Ti3C2 catalyst exhibited outstanding photo-Fenton-like performances towards the degradation of cationic organic dyes (methylene blue, rhodamine B, basic fuchsin) in a wide pH range of 3.04–10.02. Radical trapping and electron paramagnetic resonance experiments revealed that surface-bound hydroxyl radicals (OH), superoxide radicals (O2−), and photogenerated holes (h+) were the dominant species in the Ti3C2/H2O2/Visible-light system. Density functional theory calculations confirmed that TiO2/Ti3C2 Schottky heterojunctions not only promoted the separation of photogenerated carriers, but also facilitated the desorption of hydroxyl groups (–OH) from the decomposition of H2O2, thereby increasing the yield of reactive species (OH, O2−, and h+).