Objective: The aim of the present study was to explore the use of complementary consent methodologies to support a potentially vulnerable group of people, namely those aging with intellectual disability, to provide personal input. It was premised on the view that processes to determine capacity for consent, appropriately modified to account for individual capabilities and current circumstances, could facilitate meaningful participation in the development of personal health care plans of people previously excluded from contributing. Methods: The present descriptive case study research was undertaken in New South Wales, Australia. A seven-step process for determining capacity for consent was developed, and 10 participants aged between 54 and 73 years with lifelong intellectual disability and health comorbidities were involved. A variety of assistive communication tools was used to support individuals to demonstrate their capacity for giving informed consent. Results: After being provided with tailored support mechanisms, seven participants were considered to meet all seven components for determining capacity for consent. Three participants were deemed not to have capacity to give consent regardless of the type of support provided. Conclusions: Three critical factors for facilitating personal involvement in decision making for individuals with an intellectual disability were identified: (1) defining consent specifically for the target outcome; (2) outlining the criteria needed for consent to be obtained; and (3) using appropriately modified alternative communication mechanisms as necessary.