•Biological control is an underutilised tool for controlling parasitic nematodes.•In-feed treatment with nematophagous fungi can reduce larval numbers post-excretion.•The fungus Duddingtonia flagrans is the first commercial biological control agent.•Dung beetles and earthworms can help to reduce infective stages on pasture.•Integrated parasite management facilitates sustainable parasite control. Gastrointestinal nematodes (GIN) are a cause of significant losses in animal production worldwide. In recent years, there have been important advances in the biological control of GIN of ruminants and horses. While these measures are still relatively under-utilised in practice, interest will undoubtedly grow due to the emergence of drug resistant parasite populations, the rise in demand for organically farmed products (which does not allow prophylactic use of drugs, including anthelmintics) and legislation, which regulates and restricts the use of anthelmintics. This review provides an overview of the most promising biocontrol agents of GIN of grazing animals including nematophagous fungi, dung beetles, earthworms, predacious nematodes and nematophagous mites. Recent advancements in these fields are evaluated, and the potential reasons for the delayed development and slow uptake of biocontrol agents are discussed. It is now widely believed that no method of GIN control is sustainable alone, and a combination of strategies (i.e. integrated pest management) is required for long term, effective parasite control. This review shows that, although their efficacies are lower than those of conventional anthelmintics, biological control agents are an important adjunct to traditional GIN control.