Oceanic island ecosystems contain a disproportionate number of Earth’s terrestrial species, many of them endemic or indigenous to only one or a few islands. Consequently, the importance of islands in the quest to protect terrestrial biodiversity has been increasingly recognized and included in global environmental agreements. Nevertheless, oceanic island ecosystems remain extremely vulnerable to anthropogenic disturbance and its impacts, particularly in terms of the uncontrolled spread of introduced species, so-called biological invasions, leading to substantial biodiversity loss and fundamental changes in ecosystem functioning and structure. The South Pacific region is a hotspot of biodiversity but also has the world’s highest concentration of invasive alien plant species. Although the issue of biological invasions has been increasingly acknowledged by local governments and international agreements, invasive alien species are often not monitored properly on Pacific islands. Furthermore, knowledge of the potential impact of invasive alien species regularly does not result in on-the-ground action, adding to the growing extinction threat. This inaction persists despite international and national efforts for sustainable use and nature conservation of terrestrial biodiversity in the region’s Small Island Developing States. We illustrate this problem with two relatively recent biological invaders in Fiji: the ivory cane palm (Pinanga coronata) and the green iguana (Iguana iguana). We use these examples to examine the potential consequences of continuing inaction, despite awareness in relevant government departments, for native forest biodiversity and human livelihoods. Through an examination of the institutional background, we discuss steps towards good governance and sustainable development of terrestrial biodiversity in the Small Island Developing States of the tropical South Pacific, where on-the-ground action to control, eradicate, and prevent invasive alien species is desperately needed.