Background: Whilst the potential benefits of exercise rehabilitation in cancer survivorship are plentiful, recruitment to survivorship rehabilitation trials remains suboptimal. There is growing evidence that Public and Patient Involvement (PPI) initiatives can increase the rate of recruitment to research. This study within a trial (SWAT) will examine if participant information co-developed by patients and their families can lead to greater recruitment rates, retention and understanding of the Rehabilitation Strategies in Oesophago-gastric and Hepatopancreaticobiliary Cancer (ReStOre II) trial when compared to standard participant information. Methods: This SWAT will be carried out over two phases. Phase I will utilise qualitative methods to develop (Phase Ia) and refine (Phase Ib) the new participant information. Phase Ia will recruit up to 20 survivors of upper gastrointestinal or hepatopancreaticobiliary cancer, or their family members, to take part in a focus group or interview to develop the new participant information. Focus groups/interviews will be recorded, transcribed verbatim and analysed thematically. In Phase Ib, participants will return for a second focus group/interview to refine the participant information. Once finalised, the participant information will be submitted to ethics for approval. In Phase II, potential participants for the ReStOre II trial will be randomly assigned to receive either the standard or patient and family co-developed participant information. The two forms of participant information will be compared by recruitment and retention rates, and participant understanding of the trial (Decision-Making Questionnaire). Discussion: We anticipate that engaging with patients and their families to develop participant information will help to increase patient understanding of the ReStOre II trial and therefore recruitment and retention rates. The results of this SWAT will indicate the usefulness of this strategy for optimising recruitment to exercise rehabilitation trials in cancer survivorship. Registration: SWAT: Northern Ireland Hub for Trials Methodology Research SWAT Repository Store (SWAT-100). ReStOre II: ClinicalTrials.gov (NCT03958019).