Noncommunicable diseases (NCDs) contributed to deaths of at least 43 million people globally in 2021, equivalent to 75% of all non-pandemic-related deaths1. Major modifiable NCD risk factors include low physical activity and poor diet2. Conducting lifestyle clinical trials online can provide a practical and scalable way to test lifestyle interventions aimed at reducing the burden of these diseases. However, being a novel method of trial delivery, online clinical trials present several new major challenges and considerations to be addressed. A systematic scoping review of published review papers was carried out to map the digital delivery methods in online lifestyle intervention trials, focusing on technologies, recruitment, engagement and retention strategies, and reported strengths, limitations, and future directions. Using PRISMA-ScR guidelines3, PubMed, EMBASE, CINAHL, Web of Science, and Scopus were searched for reviews published between January 2013 and May 2025. Eligible reviews (n=39) included digital interventions targeting diet, physical activity, or both, for lifestyle improvement, chronic disease prevention or management. Papers excluded from the review were predominantly (>50%) related to hybrid, telehealth, or acute condition interventions. The review findings indicated that the most common hardware used in online lifestyle clinical trials were smartphones and wearables, with the most frequent software modes being web-based platforms, mobile apps, and SMS. Successful engagement strategies often integrated behaviour changes techniques, such as goal setting, self-monitoring, personalised feedback, and human support into the intervention design, or had behaviour change techniques as a feature of the technology itself. Reported strengths of conducting clinical trials online included improved accessibility, scalability, cost-efficiency and personalisation, whereas limitations discussed were poor participant engagement and retention, digital literacy barriers, and technological advancements progressing faster than they can be evaluated. Interventions that used theory-based designs, particularly those using Social Cognitive Theory, the Transtheoretical Model, and the Theory of Planned Behaviour, were reportedly successful in improving behavioural outcomes. The review highlighted the critical role of integrating theory and behaviour change techniques into intervention and technology design to optimise engagement, retention, and overall success in online lifestyle clinical trials. Overall, this review shows that online delivery of lifestyle intervention trials is a feasible and potentially advantageous method to implement trials as it can improve reach, increase scalability, be cost-efficient, and allow more personalisation. To continue to improve the conduct of online clinical trials, future research should address the identified challenges, including promoting participant engagement, giving equitable access to clinical trials, ensuring data privacy and security, improving intervention fidelity, and adapting to rapidly evolving technologies. Additionally, applying evidence-based designs and technologies that utilise behaviour change techniques and are grounded in behavioural theory, likely would be useful to improve the conduct of online clinical trials focused on diet and physical activity focused interventions.