Context: Internationally, registered nurses (RNs) are increasingly working in team-based primary care settings. Despite this, there remains a lack of evidence about the effectiveness of their contributions to outcomes. A systematic review of the literature is essential to inform further integration and optimal utilization of RNs within primary care teams. Objective: The purpose of this systematic review was to synthesize the evidence regarding the effectiveness of RNs in primary care on processes of care and outcomes. Study Design: Systematic review in accordance with Joanna Briggs Institute methodology. Dataset: A comprehensive search of relevant databases (e.g. CINAHL, Medline Complete) was conducted using relevant subject headings and keywords. Additional grey literature was identified through Google Scholar, nursing organization websites, and searches of key journals/authors. Population studied: An initial 6408 titles/abstracts were screened for relevancy, resulting in 268 full-text articles to be assessed. Eligible studies reported on any quantitative outcome of an intervention/process delivered by RNs in primary care. All studies were published in English. No date or location restrictions were applied. Risk of bias was assessed using the Integrated Quality Criteria for Review of Multiple Study Designs tool. Outcome Measures: The final review consisted of 26 studies. Extracted data included information on study design, data collection methods, primary care settings, RN interventions, and outcomes. Results: The results yielded 20 distinct outcomes, identified at either the patient-level (n=9) or care delivery/system-level (n=11). Patient outcomes consisted of self-report measures (e.g. satisfaction, quality of life) and clinically-assessed health indicators (e.g. HbA1C, blood pressure). Care delivery/system outcomes examined the quality of RN care provision and broader health system measures (e.g. service utilization, cost). RN-delivered care was equivalent to or better than care delivered by other providers, specifically with respect to chronic disease management, smoking cessation, and wellness counselling. There was a high level of reported patient satisfaction regarding RN-led care. Conclusions: This review provides important evidence on the effectiveness of RNs on primary care outcomes. Strengthened assessment approaches and consensus on outcome measures are needed to address healthcare challenges and support further evaluation.