Many transgender and gender diverse (TGD) people use the internet to find ways out of isolation, network, and share information on health-related topics. Thus, e-health services could reduce the health burden of TGD people and facilitate access to health care. Following the PRISMA guidelines, we conducted a systematic review on e-health approaches that could improve trans health care (i.e., services directly for TGD people or training programs for health care professionals, HCPs) and their effectiveness, acceptability, and feasibility. We searched PubMed, Web of Science, and PubPsych databases for publications from January 2000 to June 2021 with final updates before publication. The systematic review identified e-health services across 27 studies from 8 different countries. Few studies evaluated e-health services exclusively for TGD people. However, use of an e-health service was found to be effective and beneficial: TGD people improved in health-related outcomes, and HCPs improved in professional expertise. Service users find e-health services helpful and easy to integrate into their daily lives. Recommendations for further development of e-health services in trans health care are provided. In the future, given the rapidly evolving e-health research and care field, new treatment approaches for TGD people should be subject to ongoing evaluation and development.