Up-to-date information on the distribution of alien species is essential for evidence-based management. However, routine monitoring is resource intensive. This has led to regional biases in the availability of information on invasions, with little understanding of invasions in many developing regions, including Africa. This knowledge gap, particularly problematic for marine protected areas (MPAs), challenges the ability of African states to meet their obligations under the Global Biodiversity Framework (GBF) Target 6. This study drew on freely available global databases (Protected Planet; World Register of Introduced Marine Species; World Register of Marine Species) and citizen science data (iNaturalist) to provide novel insights into marine alien species in African MPAs. A total of 27 species were recorded within 17 MPAs across seven countries. The potential threat posed to these MPAs was assessed using the EICAT and SEICAT impact schemes. Worryingly, species known to have impacts of massive or major magnitude were documented in nine MPAs (Table Mountain National Park, Robben Island, Sixteen Mile Beach, Langebaan Lagoon, Namaqua National Park – all in South Africa); Namibian Islands (Namibia); Ilhas Formosa, Nago and Tchedia (Urok) (Guinea-Bissau); Banc d'Arguin National Park (Mauritania); Massa (Morocco)). When used in conjunction with curated databases, iNaturalist offered cost-effective and verifiable records of some alien species in under-surveyed MPAs. By leveraging data from disparate databases, this study improves our knowledge of the scale of invasions in African MPAs and provides a foundation upon which States can prioritise monitoring within their MPA networks. Ultimately, these data could support the development of targeted routine monitoring programmes which could assist the management of marine invasions and the attainment of GBF Target 6.