Background: Digital mental health (dMH) treatments have garnered much attention for increasing access to treatment, yet real-world engagement with these treatments remains a challenge. In upscaling these treatments, we need to ensure that they are equitable and do not exclude groups who already experience inequities in healthcare, such as people with lower health literacy. To this end, we aimed to co-develop recommendations for the design and delivery of dMH treatments for people with a variety of health literacy levels. Methods: Drafted recommendations were based on a thematic analysis of 357 free-text comments (likes, dislikes/other suggestions) from 213 people (n=80 lower, and n=133 higher health literacy) who had completed unguided internet-delivered cognitive behaviour therapy (iCBT) for depression and anxiety, as part of a trial. The initial set of drafted recommendations were iteratively modified and refined based on a review by a multidisciplinary project team with professional and lived-experience expertise (n=9) and focus group consultations with people with relevant lived experience (n=8). Results: The co-development process resulted in seven final recommendations: 1) Focus on informative and practical content; 2) Prioritise accessibility and ease of use; 3) Structure content in a progressive, layered way; 4) Enhance interactivity and engagement; 5) Employ strategies to enhance motivation and accountability; 6) Consider participants’ emotional wellbeing; 7) Incorporate diverse modes of delivering content. Most recommendations were based on comments from people with lower and higher health literacy, as opposed to being mainly one group or the other. Conclusions: These recommendations advance both research and practice by outlining a flexible and practical framework for dMH treatment developers and service providers to meet the preferences and needs of people with diverse health literacy strengths and needs. Further research is needed to determine the feasibility and impact of implementing these recommendations across different dMH treatment delivery formats, settings, and populations.