A systematic review and meta-analysis examined the impact of clinical pharmacist-led interventions (medication education, medication monitoring, adherence support, relapse monitoring, and collaboration with psychiatrists) on patients with bipolar I disorder. PubMed, Embase, PsycINFO, Scopus, Web of Science, and the Cochrane Library were searched for studies from January 2000 to August 2025, including randomized controlled trials and non-randomized intervention studies. Five studies met the criteria, four provided quantitative data. The interventions significantly improved medication adherence compared to usual care (MD = 1.47 [95% CI: 1.35–1.59], p < 0.00001). They reduced the number of relapses (OR = 1.94 [95% CI: 1.15–3.23], p = 0.01; I² = 38% from two studies). Improvements in quality of life were observed (SMD = –1.89 [95% CI: –4.95–1.20], p = 0.21; I² = 90%), evidence for a reduction in hospital admissions was limited but favourable. The evidence is preliminary due to the small number of studies and samples.