Multiple sclerosis (MS) is a complex immune-mediated disease with no currently known cure. There is growing evidence to support the role of diet in reducing some of the symptoms and disease progression in MS, and we previously developed and tested the feasibility of a digital nutrition education program for people with MS. The aim of this study was to explore factors that influenced engagement in the digital nutrition education program, including features influencing capability, opportunity and motivation to change their dietary behaviours. Semi-structured interviews were conducted with people who had MS, and who completed some or all of the program until data saturation was reached. Interviews were analysed inductively using thematic analysis. Themes were deductively mapped against the COM-B (Capability, Opportunity, Motivation, Behaviour) behaviour change model. Sixteen interviews were conducted with participants who completed all (n = 10) or some of the program (n = 6). Four themes emerged: (1) acquiring and validating nutrition knowledge; (2) influence of time and social support; (3) getting in early to improve health and (4) accounting for food literacy experiences. This is the first online nutrition program with suitable behavioural supports for people with MS. It highlights the importance of disease-specific and evidence-based nutrition education to support people with MS to make dietary changes. Acquiring nutrition knowledge, coupled with practical support mechanisms, such as recipe booklets and goal setting, emerged as crucial for facilitating engagement with the program. When designing education programs for people with MS and other neurological conditions, healthcare professionals and program designers should consider flexible delivery and building peer support to address the needs and challenges faced by participants. Members of the MS Nutrition Research Program Stakeholder Reference Group, which includes people with MS and MS health professionals, provided input during the development of the nutrition education program and study design stages.