Objectives Internet‐ and mobile phone‐based psychological interventions have the potential to overcome many of the barriers associated with accessing traditional face‐to‐face therapy. Self‐injurious thoughts and behaviors (STB) are prevalent global health problems that may benefit from Internet‐ and mobile‐based interventions. We provide a systematic review and meta‐analysis of studies evaluating mobile‐ and Internet‐based interventions for STB, including nonsuicidal self‐injury (NSSI). Methods Online databases (PsycINFO, Web of Science, Medline) were searched up to March 2019 for single‐arm and controlled trials of Internet‐ or mobile‐based interventions for STB. The potential for bias was assessed using the Cochrane risk of bias tool. Results Twenty‐two eligible trials were identified. The research was limited by a lack of controlled designs and small samples. Evidence supports the acceptability of interventions. There is preliminary evidence that these interventions are associated with a decline in STB. A meta‐analysis suggested a positive treatment effect on suicidal ideation when compared to treatment as usual, but not when trials with active controls were also considered. Conclusions Overall, Internet‐ and mobile‐based interventions show promise and further controlled trials are warranted, focusing on behavioral outcomes (NSSI, suicidal behavior). This review was preregistered with PROSPERO (CRD42017074065).