OBJECTIVE: This paper describes the development and implementation of an exercise intervention to prevent falls within The Prevention of Fall Injury Trial (PreFIT), which is a large multi-centred randomised controlled trial based in the UK National Health Service (NHS). DESIGN: Using the template for intervention description and replication (TIDieR) checklist, to describe the rationale and processes for treatment selection and delivery of the PreFIT exercise intervention. PARTICIPANTS: Based on the results of a validated falls and balance survey, participants were eligible for the exercise intervention if they were at moderate or high risk of falling. INTERVENTIONS: Intervention development was informed using the current evidence base, published guidelines, and pre-existing surveys of clinical practice, a pilot study and consensus work with therapists and practitioners. The exercise programme targets lower limb strength and balance, which are known, modifiable risk factors for falling. Treatment was individually tailored and progressive, with seven recommended contacts over a six-month period. Clinical Trials Registry (ISCTRN 71002650).