Background: As the role of Patient and Public Involvement contributors expands to all stages of the research cycle, there is increasing demand for training that meets the needs of this diverse population. To help meet this demand the National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care, Yorkshire and Humber, worked with members of the public to develop a bespoke training package. The University of Huddersfield’s Public Partnership Group were invited to host the training and undertake an independent evaluation. Methods: Participatory action research was used to structure the evaluation, such that participants in the training and public members of the evaluation team were co-collaborators with a robust, significant and visible share in the process. This is evidenced by public team members’ roles in undertaking the majority of data gathering, including surveys, non-participant observation and interviews, and analysis, engaging in all reflective discussions, leading on producing a formal report and contributing significant sections of this paper. The evaluation was approved by a University ethics panel. Public involvement consisted of the 13 participants who received the training, and 3 of the 6 members of the evaluation team. Data collection took place between November 2017 and March 2018. Results: The evaluation found that participants understood more about the research process from attending the training, gaining greater confidence in their ability to volunteer to get involved. It also highlighted the difficulties of meeting the training needs of a diverse group with varying experiences and expectations. Skilful facilitation was needed to maintain pace, whilst engaging people with different levels of interest and knowledge. The management of the environment to maximise comfort and involvement was important. Early feedback to the delivery team enabled timely updating of the package. Involvement in the evaluation was initially daunting for the three public members of the team, but hugely enjoyable and fulfilling, as well as enriching the process and outcomes. In particular, public involvement in the analysis and interpretation stages increased the authenticity of the evaluation findings. Conclusions: This evaluation validated the training package and demonstrated the value and impact of Public Involvement at all levels in research.