Abstract Background Between 1990 and 2017, stroke cases nearly doubled, ranking as the second leading cause of death and disability globally. Inadequate physical activity (PA) is a leading risk factor. Recent guidelines advise stroke survivors to follow population-based PA guidelines. Given stroke heterogeneity personalised PA interventions are recommended. Therefore, this study used a Sequential Multiple-Assignment Randomized Trial (SMART) design to develop an adaptive mHealth intervention to improve PA post-stroke. Methods This SMART is in progress, with recruitment completed and follow-up data ending November 2024. A 12-week intervention programme was developed incorporating public patient involvement (PPI), empirical evidence and behavioural change theory to increase participation in Structured Exercise (SE), Lifestyle Physical Activity (LPA), or both. The study enrolled 54 ambulatory, community-dwelling people who were randomly assigned to either SE or LPA treatment groups. Participants used Fitbit Inspire 2 devices to monitor step counts and set personalized weekly step goals. At six weeks post-randomisation, participants were evaluated and classified as responders or non-responders based on their step count target achievement. Non-responders were re-randomized to switch treatments or augment their current regime with an additional intervention. Responders maintained their original treatment protocol. Primary outcomes address recruitment, retention and adherence rates. Secondary outcomes encompass overall health. Results Preliminary results include 54 participants (56% male) aged 51.58 (± 15.12) with Ischaemic (44%), Haemorrhagic (28%) or unknown (28%) stroke type at baseline. The mean weekly step was 7046 (±3797) while the mean Fatigue Severity Scale score was 38.02 (± 14.60). Participants had a mean Hospital Anxiety and Depression Scale score of 12.33 (± 6.98). Additionally, the mean Stroke Specific Quality of Life was 155.04 (58.84). Conclusion This is the first trial to use a SMART to design an adaptive intervention post-stroke internationally. Findings will inform the development of a PA intervention and subsequently will be evaluated against treatment as usual in a definitive trial.