Background: People with severe to profound intellectual disabilities experience similar or higher levels of depression than those with more mild intellectual disabilities. Yet, there is an absence of evidence about how to adapt existing psychological therapies for this population. Method: A behavioural activation intervention (BeatIt) for people with mild to moderate intellectual disabilities was adapted for people with severe to profound intellectual disabilities and depression. Key considerations include: (i) beginning with a more in-depth assessment process; (ii) including the person in session activities and developing a relationship with them; (iii) formulation and the use of film to document the link between activity and mood; and (iv) addressing barriers to change at an individual and inter-personal level and considering how the carer could support the person's engagement in activity. Results: Successfully adapting BeatIt represents a first step towards gathering evidence about the effectiveness of behavioural activation for people with severe to profound intellectual disabilities.