© The Author(s) 2019. Background: Globally, the poor activity level of adolescent girls is a public health concern. Little research has involved adolescents in the design of interventions. This study assessed the feasibility of involving girls in the co-creation of an activity programme. Methods: Thirty-one students (15¿17 years old) were recruited from a post-primary school. The Behaviour Change Wheel guided intervention design, providing insights into participants¿ capability, opportunity and motivation for change. Step counts and self-reported physical activity levels were recorded pre- and post-intervention. Feasibility benchmarks assessed recruitment, data collection, acceptability and adherence. Results: Activity and educational sessions were delivered for six weeks during physical education class. Average attendance was 87% (benchmark = 80%). Eligibility was 61% (benchmark = 60%). There was a 100% retention rate (benchmark = 90%). All participants (n = 31) completed baseline measures and 71% (n = 22) completed post-measures. 54% (n = 17) of students completed pedometer measurements, with 32% (n = 10) having complete data. Average daily steps were 13,121 pre-intervention and 14,128 post-intervention (p > 0.05). Data collection was feasible, receiving a mean score > 4/5 (benchmark > 3.5/5). Conclusions: The Behaviour Change Wheel can be used to co-create an activity programme with adolescent girls. Predetermined benchmarks, except for pedometer recordings, were reached or exceeded, providing evidence for the need of a randomised controlled trial to test effectiveness.