Background: Chat-based hotlines use online messaging services or popular chat applications such as WhatsApp, Facebook Messenger, and WeChat, to connect users to trained health providers or staff. Chatbased hotlines can provide real-time communication between health providers and patients. Methods:The evidence for chat-based hotlines for health promotion has not been reviewed systematically.Electronic databases (PubMed, Cochrane Database, Google Scholar) were searched to identify Englishlanguage studies describing original research published from 2009 to 2020. This review was registered with Prospero Register of Systematic Reviews (ID: CRD42020156670).Results: Twelve publications met our criteria. Ten studies reported on user characteristics, eight on comparing use of chat-based hotlines with different modes of support, six on health outcomes and six on user satisfaction. Included studies report that chat-based hotlines have been used primarily for crisis and emotional support in high-income countries. Chat-based hotlines using instant messenger applications were preferred over other modes of services such as email, text messaging, voice calls, and face-to-face counselling.Evaluations of health outcomes, although limited in rigor due to mostly observational study designs, indicate mostly positive and statistically significant effects on mental health outcomes such as anxiety, depression, well-being and suicidality. User satisfaction with chat-based hotlines were moderately high.Conclusions: Chat-based hotlines may be effective ways to deliver crisis support services in high income settings. They may have the potential to be effective in low-and middle-income countries to expand the reach of mental health and crisis support services although such services have not yet been publicly evaluated.