Background: This participatory action research (PAR) project involved a collaboration with a self-advocacy group of people with intellectual disabilities that sought to build group capacity for advocacy. Materials and Methods: This study used a focus group, sustained participatory engagement and a reflexive process to gather qualitative and quantitative data over 15 months. All methods were adapted to ensure accessibility and to support active participation. Results: The collaboration generated action products, including tools to support advocacy and an accessible action and reflection process. Research findings suggest that active participation is essential for group control, but alone does not automatically lead to control. The manner in which supports are provided, including member supports, advisor supports, strategy supports and systems supports, influences the extent to which members have a sense of control over decision making and participation and thus, improved capacity for advocacy. Conclusions: A PAR approach can be used to increase a group's capacity for advocacy and meaningfully involve self-advocacy groups in participatory research that leads to change.