The role of clinical pharmacists in primary care has evolved significantly in recent years, particularly in the management of long-term conditions such as atrial fibrillation (AF) and type 2 diabetes mellitus (T2D). Despite their growing involvement in prescribing and optimising patient care, the contributions of clinical pharmacists, as well as the challenges they face within general practice settings, remain underexplored. This thesis evaluates the effectiveness of pharmacist-led interventions in optimising therapeutic outcomes in AF and T2D and examines their prescribing practices using behavioural frameworks such as the Theoretical Domains Framework (TDF). The overall aim of this thesis is to assess and explore the role of clinical pharmacists in general practice in England, focusing on their impact on the management of AF and T2D, and identifying the challenges they face in prescribing and managing patient care. The thesis adopts both qualitative and quantitative approaches, including systematic literature reviews, retrospective observational studies, and semi-structured interviews with clinical pharmacists. Data from electronic health records in general practice were analysed to evaluate the impact of pharmacist-led interventions on clinical outcomes. Additionally, the Theoretical Domains Framework (TDF) was applied to explore pharmacists' prescribing behaviours in managing AF and T2D.The systematic review highlighted the varied roles of clinical pharmacists in general practice, with an emphasis on medicines optimisation, particularly in the management of long-term conditions such as AF and T2D. While national policies support pharmacist-led medication reviews, the evidence on their impact on patient outcomes remains mixed, indicating the need for further research. A retrospective observational study demonstrated that pharmacist-led interventions increased the appropriate use of oral anticoagulants (OAC) in AF patients, reducing inappropriate dosing and improving patient safety. Pharmacist interventions led to a 6% increase in Direct Oral Anticoagulant (DOAC) prescribing and reduced inappropriate use to 1.5%. The qualitative exploration of pharmacists' prescribing practices in AF management revealed barriers such as limited access to patient records and insufficient training. However, pharmacists employed strategies such as professional development to overcome these challenges. In a separate retrospective study, pharmacist-led interventions significantly improved key diabetes outcomes, including HbA1c, blood pressure, and cholesterol levels in T2D patients. The proportion of patients achieving all three clinical targets (HbA1c, BP, and cholesterol) increased from 2.4% to 23.4%. Interviews with prescribing pharmacists involved in T2D management identified themes such as confidence, professional identity, and continuous learning, with more experienced pharmacists demonstrating greater competence in managing complex cases. Less experienced pharmacists highlighted the need for additional support and mentorship. This thesis underscores the critical role of clinical pharmacists in improving patient care in general practice, particularly in the management of AF and T2D. Pharmacist-led interventions were effective in optimising therapy and achieving better clinical outcomes. However, challenges such as limited access to resources, training gaps, and issues surrounding professional identity must be addressed to further enhance their role. The findings provide valuable insights for policymakers and healthcare leaders seeking to maximise the potential of pharmacists in primary care, with implications for improving patient outcomes and alleviating pressure on general practitioners.