BACKGROUND: Physical activity (PA) is beneficial for all people; however, people affected by multiple sclerosis (MS) find regular PA challenging. These people may include individuals with advanced disabilities and their care partners. OBJECTIVE: The objective of this study is to determine the feasibility of a dyadic PA intervention for people with advanced MS and their care partners. METHODS: This study is a randomized controlled feasibility trial of a 12-week intervention, with 1:1 allocation into an immediate intervention condition or delayed control condition. A target of 20 people with MS-care partner dyads will be included. The outcomes will be indicators of process, resources, management, and scientific feasibility. Participant satisfaction with the intervention components will be evaluated using a satisfaction survey. The subjective experience of participation in the study will be explored using semistructured interviews. RESULTS: The project is funded by the Consortium of Multiple Sclerosis Centers. This protocol was approved by the Ottawa Hospital Research Ethics Board (20190329-01H) and the University of Ottawa Research Ethics Board (H-09-19-4886). The study protocol was registered with ClinicalTrials.gov in February 2020. The findings of this feasibility trial will be disseminated through presentations at community events to engage the MS population in the interpretation of our results and in the next steps. The results will also be published in peer-reviewed journals and presented to the scientific community at national and international MS conferences. CONCLUSIONS: The data collected from this feasibility trial will be used to refine the intervention and materials in preparation for a pilot randomized controlled trial. TRIAL REGISTRATION: ClinicalTrials.gov NCT04267185; https://clinicaltrials.gov/ct2/show/NCT04267185. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): PRR1-10.2196/18410.