The migration-development discourse has been subject to much policy and academic debate in the past decades. In recent years, there is growing consensus that migration can deliver ?triple wins? for migrants, sending countries and receiving countries, yet there is also caution that these ?wins? are not automatic and may remain elusive unless conducive policies are present in both sending and receiving countries. Deducing this nexus is particularly important for Pacific Island Countries (PICs) as labour mobility presents one of the few viable opportunities for sustainable development in the region. From an international trade perspective, the gains from trade lies in the exploitation of differences in factor endowment ratios and preferences, and the largest difference that PICs can exploit is in the export of its workers, particularly Pacific low-skilled workers. This thesis seeks to contribute to the understanding of the migration-development nexus by determining how the development impact of labour mobility in Pacific Island sending countries can be enhanced. Drawing on the static theory of the effects of international trade on household livelihood and the New Economics of Labour Migration theory, this thesis uses a case study of Tonga?s participation in the Australian Seasonal Worker Program (SWP) to examine the exogenous factors which affect the generation and transfer of the economic development gains from labour mobility in Pacific Island sending countries. The research adopts a mixed-methods research strategy consisting of quantitative surveys of over 520 SWP households and migrants, 76 informant interviews of key stakeholders in Australia and Tonga, and secondary data analysis of migration and development data in the region. Key findings indicate that the development gains from labour mobility are channeled through the remittances that migrants transfer and the skills they acquire during migration. These returns were found to be linked closely with the sending country?s stock of migrants yet the size of these flows was affected by a number of exogenous factors prevalent in both the sending and receiving countries. The research also identified that the returns from labour mobility were largely private transfers and therefore the positive impact of these returns on economic development in sending countries is contingent on the transfers made by migrant households for the productive capacity development of sending economies, through household income diversification. Analysis of qualitative and quantitative data obtained from SWP households and migrants in Tonga and Australia revealed that the rate of household income diversification facilitated by the SWP is low thus suggesting that the positive impact of the programme on economic development in Tonga is limited. The research found that enhancing the development impact of labour mobility in Pacific sending countries require targeted policies to: address labour market access barriers to Pacific workers, particularly low-skilled and semi-skilled labour migrants; reduce constraints to the flow of remittances to households and the transfer of skills acquired during migration; and facilitate higher rates of household income diversification including through increased labour participation and business investments. Addressing these constraints necessitates effective cooperation between Pacific Island sending countries and receiving countries such as Australia and New Zealand. Regional Trade Agreements (RTAs) such as the PACER Plus, and Bilateral Labour Agreements (BLAs) such as the SWP, are proposed as important opportunities for forging and developing this required level of cooperation. The research found that these agreements can interactively contribute to enhancing the development impact of labour mobility in Pacific sending countries through a framework where their complementary roles are developed to effectively respond to development needs in the Pacific.