Halogenated organic pollutants (HOPs) are causing a significant environmental and human health crisis due to their high levels of toxicity, persistence and bioaccumulation. Urgent action is required to develop effective approaches for the reduction and reuse of HOPs. Whereas current strategies focus primarily on the degradation of HOPs, repurposing them is an alternative approach, albeit a challenging task. Here we discover that alkyl bromide can act as a catalyst for the transfer of chlorine using alkyl chloride as the chlorine source. We demonstrate that this approach has a wide substrate scope, and we successfully apply it to reuse HOPs that include dichlorodiphenyltrichloroethane, hexabromocyclododecane, chlorinated paraffins, chloromethyl polystyrene and poly(vinyl chloride) (PVC). Moreover, we show that the synthesis of essential non-steroidal anti-inflammatory drugs can be achieved using PVC and hexabromocyclododecane, and we demonstrate that PVC waste can be used directly as a chlorinating agent. Overall, this methodology offers a promising strategy for repurposing HOPs.