Abstract Background The built environment is a major determinant of health. This research examined the process of implementing a health impact assessment (HIA) of a city development plan, using HIA guidance developed by Institute of Public Health Ireland. HIA is an established approach to facilitate a Health for All Policy approach and is a practical tool used to appraise the potential health effects of a policy, programme or project prior to implementation. Methods This mixed methods study underpinned by action research and implementation science frameworks, explored the process and experiences of undertaking an HIA on the Cork City Development Plan (2022-2028). A total of 36 stakeholders across a variety of institutions, sectors, and including members of the public, were involved in the HIA. Results We found there was an appetite for HIA’s use to facilitate cross sectoral working to identify, mitigate, and address health inequalities. Data derived from interviews, surveys and workshops indicate that while most stakeholders involved saw the value HIA could bring to their work, further efforts are required to realise the benefits of HIA as a decision-support tool. Barriers included lack of familiarity of HIA across sectors, and for those involved in carrying out the HIA, lack of adequate training, time and access to local data. Conclusions HIA can contribute to embedding a Health for All Policies approach, however, greater effort from the public health professionals is required to advocate for HIA as a tool to influence policy. Our results suggest that its practical application requires (i) intersectoral training on HIA that supports a broader understanding of the social determinants of health, (ii) knowledge of the purpose and remit of the policy, plan or programme being appraised and (iii) ensuring a broad range of relevant expertise and experience on the steering group tasked with leading the HIA. Key messages • HIA can contribute to embedding a Health for All Policies approach. • Stakeholders do see the value that HIA can bring to their work, however, further efforts are required to realise the benefits of HIA as a decision-support tool.