Background The latest global figures show that 55 million persons lived with major neurocognitive disorders (MNCDs) worldwide in 2021. In Quebec, Canada, most of these older adults are cared for by family physicians in interdisciplinary primary care clinics such as family medicine groups (FMG). When a person has a MNCD, taking potentially inappropriate medications or polypharmacy (5 different medications or more) increases their vulnerability to serious adverse events. With the recent arrival of pharmacists working in FMGs and their expanded scope of practice and autonomy, new possibilities for optimizing older adults’ pharmacotherapy are opening. Objective This project aims to evaluate the impact of involving these pharmacists in the care trajectory of older adults living with MNCD, in an interdisciplinary collaboration with the FMG team, as well as home care nurses and physicians. Pharmacists will provide medication reviews, interventions, and recommendations to improve the pharmacotherapy and support offered to these patients and their caregivers. Methods This 2-step mixed methods study will include a quasi-experimental controlled trial (step 1) and semistructured interviews (step 2). Older adults undergoing cognitive assessment, recently diagnosed with MNCD, or receiving care for this at home will be identified and recruited in FMGs in 2 Quebec regions. FMGs implementing the intervention will involve pharmacists in these patients’ care trajectory. Training and regular mentoring will be offered to these FMGs, especially to pharmacists. In control FMGs, no FMG pharmacist will be involved with these patients, and usual care will be provided. Results Medication use (including appropriateness) and burden, satisfaction of care received, and quality of life will be assessed at study beginning and after 6 months of follow-up and compared between groups. At the end of the intervention study, we will conduct semistructured interviews with FMG care team members (pharmacists, nurses, and physicians) who have experienced the intervention. We will ask about the feasibility of integrating the intervention into practice and their satisfaction with and their perception of the intervention’s impacts for older adults and their families. We will assess the effect of improved pharmaceutical care for older adults with or at risk of MNCDs through the involvement of FMG pharmacists and a reorganization of pharmaceutical care. Conclusions The inclusion of pharmacists in interdisciplinary care teams is recent and rising, strengthened by more substantial pharmacist practice roles. Results will inform the processes required to successfully involve pharmacists and implement developed tools and procedures transposable to other care settings to improve patient care. Trial Registration ClinicalTrials.gov NCT04889794; https://clinicaltrials.gov/ct2/show/NCT04889794 International Registered Report Identifier (IRRID) DERR1-10.2196/42577