BackgroundTo date, little is known about the sustainability and scalability ofMyDiabetesPlan, an eHealth innovation designed to facilitate shared decision-making within diabetes care. To avoid the possibility of its short-lived implementation and promote wider adoption so as to promote patient-centred diabetes care, it is critical to understandMyDiabetesPlan’s sustainability and scalability in order to ensure its long-term impact at a greater scale. We sought to identify the sustainability and scalability potential ofMyDiabetesPlanand its limiting factors.MethodsUsing a concurrent triangulation mixed-methods approach, data were collected from 20 individuals involved in the development and implementation ofMyDiabetesPlan. The National Health Services Sustainability Model (NHSSM) and the Innovation Scalability Self-administered Questionnaire (ISSaQ) were administered using a ‘think-aloud’ approach and subsequently, short semi-structured interviews were conducted. Mean aggregate scores and stakeholder-specific scores were generated for the NHSSM and ISSaQ, to quantitatively determine facilitating and limiting factors to sustainability and scalability. Content analysis occurred iteratively with qualitative data, to examine commonalities and differences with the quantitative findings.ResultsThe top facilitating factor to sustainingMyDiabetesPlanwas “Staff involvement and training to sustain the process.”, whereas the top limiting factors were: “Adaptability of Improved Process”, “Senior Leadership Engagement” and “Infrastructure for Sustainability”. The top three facilitating factors for scale-up were “Acceptability”, “Development with Theory” and “Consistency with Policy Directives.” Conversely, the top three limiting factors were “Financial and Human Resources”, “Achievable Adoption” and “Broad Reach”. Qualitative findings corroborated the limiting/facilitating factors identified.ConclusionsAddressing staff involvement throughout the dynamic care contexts, and resource constraints impacting scale-up can enhance the sustainability and scalability ofMyDiabetesPlan.As such, future plans will focus on garnering organizational leadership buy-in and support, which may address the resource constraints associated with sustainability and scalability and improve the capacity for adequate staff involvement. eHealth researchers will be able to prioritize these limiting factors from the outset of their tool development to purposefully optimize its sustainability and scalability performance.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12913-023-09618-x.