Multisectoral governance has been recognized to be vital to regulate harmful commodity industries, yet countries struggle with reaching policy coherence due to government agencies' conflicting mandates and industry interference. Limited empirical evidence is available on how interests, ideas, and institutions intersect and influence multisectoral governance in low‐ and middle‐income countries, particularly in Pacific small island developing states (PSIDS), often exploited by vested industry interests and whose non‐communicable disease crisis commands urgent action to regulate harmful commodities. This study assessed the ways interests, ideas, and institutions intersect and shape multisectoral tobacco governance in PSIDS. Interviewee data collected in Fiji and Vanuatu show that the idea of individual responsibility, the limited recognition of commercial determinants of health, the centralization of authority, and the vulnerabilities of small island developing states, (including small population, land, economy, geographic isolation, and status as a developing economy), prevent these states from achieving policy coherence in multisectoral tobacco governance.