This paper describes the people, activities and methods of consumer engagement in a complex research project, and reflects on the influence this had on the research and people involved, and enablers and challenges of engagement. The 2.5-year Integrating and Deriving Evidence Experiences and Preferences (IN-DEEP) study was conducted to develop online consumer summaries of multiple sclerosis (MS) treatment evidence in partnership with a three-member consumer advisory group. Engagement methods included 6-monthly face-to-face meetings and email contact. Advisory group members were active in planning, conduct and dissemination and translational phases of the research. Engaging consumers in this way improved the quality of the research process and outputs by: being more responsive to, and reflective of, the experiences of Australians with MS; expanding the research reach and depth; and improving the researchers' capacity to manage study challenges. Advisory group members found contributing their expertise to MS research satisfying and empowering, whereas researchers gained confidence in the research direction. Managing the unpredictability of MS was a substantive challenge; the key enabler was the 'brokering role' of the researcher based at an MS organisation. Meaningfully engaging consumers with a range of skills, experiences and networks can make important and unforeseen contributions to research success.