Economic diplomacy has become an indispensable dimension of statecraft for small, developed countries that face structural disadvantages in the global economy. For nations such as New Zealand, geographic isolation, demographic constraints, and reliance on primary exports have constrained their capacity to exert influence in global markets. Yet, in the context of deepening globalization and the proliferation of plurilateral trade frameworks, New Zealand has demonstrated a remarkable ability to transcend these constraints through strategic deployment of economic diplomacy. This study applies negotiation theory, drawing on systemic, domestic, and ideational factors to examine how New Zealand has enhanced its global economic engagement in the post-2010s, with particular emphasis on its participation in the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP). Through empirical examination of decision-making processes and trade outcomes, this study demonstrates how negotiation factors such as relative economic power asymmetries, domestic institutional capacity, and commitment to liberal trade norms shaped New Zealand’s participation and policy choices. The analysis further evaluates how CPTPP membership mitigated or reinforced structural challenges, including exposure to external shocks and reliance on agricultural exports. The findings reveal that New Zealand used the CPTPP not merely as a market-access mechanism but as a diplomatic tool to embed itself in high-standard trade governance and amplify influence within a plurilateral framework. The study thus contributes to small-state diplomacy literature by showing that strategic negotiation and institutional entrepreneurship can compensate for material constraints, positioning New Zealand as an adaptive and norm-shaping actor in the global economy.