This evaluation and impact report documents the outcomes of the Skills Development for Managing Longitudinal Data for Sharing project, delivered by the UK Data Service as part of a foundational project of Population Research UK (PRUK). The initiative aimed to strengthen the expertise of data managers and researchers across the Longitudinal Population Studies (LPS) community by addressing critical skills gaps in research data management and promoting wider data sharing. The report captures the scope, activities, outputs, and impacts of the project. It includes an assessment of training needs, lessons learnt, and detailed recommendations for future activity. It also highlights the reach and reception of the training programme, including over 300 participants from 12 countries, the development of a suite of openly available training materials, and the use of a ‘train the trainer’ model to maximise sustainability and reuse. The report serves as a comprehensive resource for stakeholders, funders, and the wider research community seeking insight into effective capacity-building for longitudinal data sharing. It was produced as the final deliverable for the project funded by the Economic and Social Research Council (ESRC) and the Medical Research Council (MRC).