Solomon Islands’ plural legal system, in which customary law operates in parallel with common law, and its practice and effects on society have drawn scholarly attention in spaces of legal studies, policy, economics, and state governance. An area that remains understudied is the dynamic nature in which landowners use Indigenous cultural heritage such as ancestral sites or genealogies as kastom evidence in courts. We explore this intersection through a critical review of the literature, Solomon Islands court judgments, and the nation’s lacking cultural heritage legislation. Two major infrastructure development projects in Solomon Islands, the Tina Hydro Project located on Guadalcanal and the Bina-Talifu Project on Malaita, are also examined to explore the nuances of state-led compulsory versus negotiated land acquisition. Fueling the perception that the customary land system is more of a hinderence than a strength to its peoples, these case studies demonstrate the fluid and unpredictable nature with which kastom evidence has been implemented in legal forums to substantiate or dispute claims. Ultimately, we argue that this largely reflects an incongruence between the British legal framework and traditional land tenure systems. Furthermore, we highlight how greater integration of archaeological expertise into legal processes of land surveying in Solomon Islands has the potential to mitigate some of these challenges.