At a London-based hospital, a validated ward-based clinical pharmacy activity collection tool has been used to monitor activities of clinical pharmacy teams across all settings, including ambulatory care services. No data confirm its representativeness for the full range of ambulatory clinical pharmacy services, and pharmacists share this concern. This study aimed to identify the range of clinical pharmacy activities in ambulatory care, assess the suitability of the existing ward-based tool for capturing these activities, and recommend modifications. Non-participant direct observations were conducted to record pharmacists' clinical activities in ambulatory clinics and multidisciplinary meetings. These observations were compared to the existing ward-based tool to identify discrepancies. Semi-structured interviews with eight ambulatory pharmacists were transcribed verbatim and thematically analysed inductively to explore the tool's representativeness of their routine clinical activities. Twenty-nine clinical pharmacy activities were observed in ambulatory services. Only fifteen were captured by the existing tool, with therapy monitoring and recommending therapeutic changes not accurately captured. Pharmacists agreed that the tool was not fully representative and included irrelevant activities. Four common uncaptured activities were multidisciplinary meeting-specific activities, arranging laboratory tests, monitoring patient outcomes, and liaising with community healthcare professionals. This study identified 33 candidate ambulatory clinical pharmacy activities. The existing ward-based tool does not fully capture the full range of ambulatory care clinical pharmacy activities, highlighting the need for an improved tool. Pharmacists recommended including the uncaptured activities. The candidate activities provide a foundation for standardised measurement of relevant ambulatory care activities to enable effective workforce deployment and improve patient outcomes.