Chemical upcycling of polyethylene (PE) can convert plastic waste into valuable resources. However, engineering a catalyst that allows PE decomposition at low temperatures with high activity remains a significant challenge. Herein, we anchored 0.2 wt.% platinum (Pt) on defective two‐dimensional tungsten trioxide (2D WO3) nanosheets and achieved hydrocracking of high‐density polyethylene (HDPE) waste at 200–250 °C with a liquid fuel (C5–18) formation rate up to 1456 gproducts ⋅ gmetal species−1 ⋅ h−1. The reaction pathway over the bifunctional 2D Pt/WO3 is elucidated by quasi‐operando transmission infrared spectroscopy, where (I) well‐dispersed Pt immobilized on 2D WO3 nanosheets trigger the dissociation of hydrogen; (II) adsorption of PE and activation of C−C cleavage on WO3 are through the formation of C=O/C=C intermediates; (III) intermediates are converted to alkane products by the dissociated H. Our study directly illustrates the synergistic role of bifunctional Pt/WO3 catalyst in the hydrocracking of HDPE, paving the way for the development of high‐performance catalysts with optimized chemical and morphological properties.