Background: During periods of illness, older adults are often accompanied to medical encounters due to complex care needs or communication barriers. While companions can play a critical role, their contributions before, during, and following medical encounters remain understudied. Objectives: To map the existing evidence on the roles played by older patients’ companions before, during and following medical encounters and their impact on patient outcomes or experience across different healthcare settings. Methods: Following Joanna Briggs Institute (JBI) methodology for scoping reviews, we searched MEDLINE, SCIE & SSCI (Web of Science), Sociological Abstracts, PsycINFO, Embase, and CINAHL for peer-reviewed English-language studies up to February 2026. We included empirical studies of older patients (age ≥ 65) and their companions (i.e., unpaid, informal caregivers) across different healthcare settings. The findings were reported following PRISMA-ScR guidelines. Results: Of 5504 studies screened, 46 were included in the final synthesis. Most companions were spouses or adult children. Studies primarily applied quantitative methods and were conducted in North America. The qualitative synthesis was organised via the concept of patient care trajectories - before, during, and following medical encounters. Eight different roles were identified. Two roles were identified before encounters, lay consultant and practical support; five during medical encounters, facilitator (contributing to language, relationship, information and decision-making), surrogate (surrogate patient and surrogate healthcare professional), assistant (providing practical and emotional sustenance), advocate and passive companion; and one role following encounters, care-giver (providing practical, clinical and emotional care-giving). During medical encounters, companions had mixed impacts, while only positive impacts were reported before or following encounters. Conclusion: Companions were found to play critical supporting roles and had measurable impacts on older patients' outcomes and experiences across different stages of the care trajectory. Practice implications: These findings provide a foundation for future research to optimise companions’ involvement during older patients’ care trajectories.