There is a lack of guidance for developing progression criteria (PC) within feasibility studies. We describe a process for co-producing PC for an ongoing feasibility study. Patient contributors, clinicians and researchers participated in discussions facilitated using the modified Nominal Group Technique (NGT). Stage one involved individual discussion groups used to develop and rank PC for aspects of the trial key to feasibility. A second stage involving representatives from each of the individual groups then discussed and ranked these PC. The highest ranking PC became the criteria used. At each stage all members were provided with a brief education session to aid understanding and decision-making. Fifty members (15 (29%) patients, 13 (25%) researchers and 24 (46%) clinicians) were involved in eight initial groups, and eight (two (25%) patients, five (62%) clinicians, one (13%) researcher) in one final group. PC relating to eligibility, recruitment, intervention and outcome acceptability and loss to follow-up were co-produced. Groups highlighted numerous means of adapting intervention and trial procedures should ‘change’ criteria be met. Modified NGT enabled the equal inclusion of patients, clinician and researcher in the co-production of PC. The structure and processes provided a transparent mechanism for setting PC that could be replicated in other feasibility studies.