Few individuals living with mental disorders around the globe have access to mental health care, yet most have access to a mobile phone. Digital technology holds promise for improving access to, and quality of, mental health care. We reviewed evidence on the use of mobile, online, and other remote technologies for treatment and prevention of mental disorders in low-income and middle-income countries. Of the 49 studies identified, most were preliminary evaluations of feasibility and acceptability. The findings were promising, showing the potential effectiveness of online, text-messaging, and telephone support interventions. We summarised the evaluations as: technology for supporting clinical care and educating health workers, mobile tools for facilitating diagnosis and detection of mental disorders, technologies for promoting treatment adherence and supporting recovery, online self-help programmes for individuals with mental disorders, and programmes for substance misuse prevention and treatment. Continued research is needed to rigorously evaluate effectiveness, assess costs, and carefully consider potential risks of digital technology interventions for mental disorders, while determining how emerging technologies might support the scale-up of mental health treatment and prevention efforts across low-resource settings.