**SUMMARY** **Background:** The Research Excellence Framework defines impact as an effect on, change or benefit to the economy, society, culture, public policy or services, health, the environment, or quality of life, beyond academia. Whether this definition captures key indicators of impact for trials is open to debate. **Aims and Objectives:** The primary aim of this study is to build consensus among a group of experts regarding key indicators of impact to support the future development of research impact assessment for trials. A body of evidence on what the trials community considers as impact could help to support better recognition of trial impact, as well as planning for impact early in the life of a trial. **Study Population:** Clinical trial experts are defined as individuals named publicly in a REF2014 impact case study highlighting a randomised trial process generating research impact. **Methods:** The Delphi technique seeks to obtain consensus on the opinions of experts through a series of structured surveys. As part of this process, the responses from each round are fed back in summarised form to the participants who are then given an opportunity to respond again to the emerging data. This study will use the digital platform Welphi.com to collect and analyse pre-existing information for ranking and/or response. **Analysis:** Indicators of impact have been generated from the [Becker Medical Library Model for Assessment of Research Impact][1] and will be evaluated using a 9-point Likert scale. Defined consensus in, consensus out, and no consensus criteria will be used to produce a final list of proposed indicators of research impact for clinical trials. Further statistical data analysis will be generated by the Welphi.com study management software. [1]: https://becker.wustl.edu/impact-assessment/model