Background Sedentary behaviour is linked to increased risk of type 2 diabetes, cardiovascular disease, musculoskeletal issues and poor mental well-being. Contact (call) centres are associated with higher levels of sedentary behaviour than other office-based workplaces. Stand Up for Health is an adaptive intervention designed to reduce sedentary behaviour in contact centres. Objectives The objectives were to test the acceptability and feasibility of implementing the intervention; to assess the feasibility of the study design and methods; to scope the feasibility of a future health economic evaluation; and to consider the impact of COVID-19 on the intervention. All sites received no intervention for between 3 and 12 months after the start of the study, as a waiting list control. Design This was a cluster-randomised stepped-wedge feasibility design. Setting The trial was set in 11 contact centres across the UK. Participants Eleven contact centres and staff. Intervention Stand Up for Health involved two workshops with staff in which staff developed activities for their context and culture. Activities ranged from using standing desks to individual goal-setting, group walks and changes to workplace policies and procedures. Main outcome measures The primary outcome was accelerometer-measured sedentary time. The secondary outcomes were subjectively measured sedentary time, overall sedentary behaviour, physical activity, productivity, mental well-being and musculoskeletal health. Results Stand Up for Health was implemented in 7 out of 11 centres and was acceptable, feasible and sustainable (objective 1). The COVID-19 pandemic affected the delivery of the intervention, involvement of contact centres, data collection and analysis. Organisational factors were deemed most important to the success of Stand Up for Health but also the most challenging to change. There were also difficulties with the stepped-wedge design, specifically maintaining contact centre interest (objective 2). Feasible methods for estimating cost-efficiency from an NHS and a Personal Social Services perspective were identified, assuming that alternative feasible effectiveness methodology can be applied. Detailed activity-based costing of direct intervention costs was achieved and, therefore, deemed feasible (objective 3). There was significantly more sedentary time spent in the workplace by the centres that received the intervention than those that did not (mean difference 84.06 minutes, 95% confidence interval 4.07 to 164.1 minutes). The other objective outcomes also tended to favour the control group. Limitations There were significant issues with the stepped-wedge design, including difficulties in maintaining centre interest and scheduling data collection. Collection of accelerometer data was not feasible during the pandemic. Conclusions Stand Up for Health is an adaptive, feasible and sustainable intervention. However, the stepped-wedge study design was not feasible. The effectiveness of Stand Up for Health was not demonstrated and clinically important reductions in sedentary behaviour may not be seen in a larger study. However, it may still be worthwhile conducting an effectiveness study of Stand Up for Health incorporating activities more relevant to hybrid workplaces. Future work Future work could include developing hybrid (office and/or home working) activities for Stand Up for Health; undertaking a larger effectiveness study and follow-up economic analysis (subject to its success); and exploring organisational features of contact centres that affect the implementation of interventions such as Stand Up for Health. Trial registration This trial is registered as ISRCTN11580369. Funding This project was funded by the National Institute for Health and Care Research (NIHR) Public Health Research programme and will be published in full in Public Health Research; Vol. 10, No. 13. See the NIHR Journals Library website for further project information.