Non-native species introductions threaten global biodiversity, ecosystems, and the services they provide. The limited capacity of developing countries to mitigate and manage biological invasions increases their vulnerability to the resulting impacts. Developing countries' lack of comprehensive information on non-native species to help formulate sound management efforts is a key challenge. Here, we provide the most comprehensive national list of established non-native species in the Philippines, along with an update on the Southeast Asian region to aid national and regional efforts in addressing the threats posed by biological invasions. Our assessment indicates that the Philippines currently hosts at least 1,029 established non-native species, the highest number among Southeast Asian countries, amidst a total of 2,528 non-native species established in the region. A taxonomic breakdown showed species of the division Tracheophyta and phylum Chordata to be the majority of established non-native species in the Philippines, most of which are found in terrestrial ecosystems. A network analysis further highlighted a high degree of similarity in the composition of established non-native species among Southeast Asian countries, with the Philippines' non-native species community most closely resembling that of Indonesia, likely due to close socio-economic ties and similar climatic niches and environmental conditions. Finally, we identified 1,499 non-native species established in Southeast Asia but not the Philippines, which may pose potential future threats for the country. We highlight the need for more comprehensive research on established non-native species in the Philippines and the Southeast Asian region, particularly taxonomic studies and research at broader geographic scales, to better understand the distribution and impact of these species and stress the critical need to address this transboundary threat.