Background: Patient “engagement” in health research broadly refers to including people with lived experience in the research process. Although previous reviews have systematically summarized approaches to engaging older adults and their caregivers in health research, there is currently little guidance on how to meaningfully engage older adults with multimorbidity as research partners. Objectives: This paper describes the lessons learned from a patient-oriented research program, the Aging, Community and Health Research Unit (ACHRU), on how to engage older adults with multimorbidity as research partners. Over the past 7-years, over 40 older adults from across Canada have been involved in 17 ACHRU projects as patient research partners. Methods: We developed this list of lessons learned through iterative consensus building with ACHRU researchers and patient partners. We then met to collectively identify and summarize the reported successes, challenges and lessons learned from the experience of engaging older adults with multimorbidity as research partners. Results: ACHRU researchers reported engaging older adult partners across many phases of the research process. Five challenges and lessons learned were identified: 1) actively finding patient partners who reflect the diversity of older adults with multimorbidity, 2) developing strong working relationships with patient partners, 3) providing education and support for both patient partners and researchers, 4) using flexible approaches for engaging patients, and 5) securing adequate resources to enable meaningful engagement. Conclusion: The lessons learned through this work may provide guidance to researchers on how to facilitate meaningful engagement of this vulnerable and understudied subgroup in the patient engagement literature.