Public health institutes have an important role in promoting and protecting the health and well-being of populations. A key focus of such institutes are the wider determinants of health, embracing the need to advocate for ‘Health in All Policies’ (HiAP). A valuable tool to support this is the health impact assessment. This study aims to support public health institutes to advocate more successfully for the use of health impact assessments and HiAP in order to promote and protect health, well-being and equity. During July 2021, a quantitative online survey was undertaken across international networks with 17 valid responses received. Semi-structured interviews were also administered with nine expert representatives and analysed thematically. In total, 64.7% (n = 11) of survey respondents were aware of health impact assessments and 47.1% (n = 8) currently conducted health impact assessments. It was noted that there are differing approaches to HIAs, with a need for a clear set of standards. Barriers to use included lack of knowledge, training and resources. Overall, 64.7% (n = 11) of survey respondents would like to do more to develop knowledge and capacity around health impact assessments. The results from this study can serve as a platform to help build knowledge, networks and expertise, to help support a ‘Health in All Policies’ approach and address inequalities which exist in all societies.