The sulfate radical-based advanced oxidation processes (SR-AOPs) are well-established and efficient techniques for the degradation of organic pollutants. Fe²⁺ is used as an environmentally friendly and cost-effective catalyst for activating peroxymonosulfate (PMS) to generate sulfate radicals (SO₄⁻˙). In some past studies, the slow process of reducing Fe³⁺ to Fe²⁺ reduced the overall reaction rate of the SR-AOP system. To overcome this challenge, in this work, we for the first time fabricated a new composite activator, FeOCl decorated by graphene quantum dots (GQDs), by a facile method for activating PMS. The experimental results demonstrate that the as-prepared FeOCl/GQD catalysts can efficiently degrade organic pollutants and kill Escherichia coli through activating PMS to generate active species. Notably, the FeOCl/(16.7 wt%) GQD composite can activate PMS to degrade organics (97.8% of RhB within 30 min) and inactivate E. coli (99.1% within 10 min) with a pH range from 3 to 11. Moreover, mechanism analyses showed that the active species were SO₄⁻˙, ˙OH, ¹O₂ and O₂⁻˙ in the FeOCl/(16.7 wt%) GQDs + PMS system, and SO₄⁻˙ and ¹O₂ were proved to be the main active species. The addition of GQDs promoted the reduction of Fe³⁺ to Fe²⁺, thereby accelerating the degradation rate. Our study suggests that the promising strategy of exploiting highly efficient AOP platforms has many applications.