The need for professional development for digital, subject-specific competencies is increasing among educators in higher education. With online teacher professional development (oTPD), this demand can be accommodated flexibly. The article presents a systematic review of the literature and evidence on oTPD for digital competencies in higher education. The purpose of the review is to identify factors that influence the effect of an oTPD programme. A total of 661 peer-reviewed articles that included empirical studies and literature reviews related to oTPD from 2010 and onwards were identified using the EBSCO and ERIC databases and screened. 57 of these were coded and included in the analysis, and 604 articles were excluded due to wrong focus, educational level, publication type, or year. The analysis identifies sixteen underlying factors that influence the effect of oTPD related to either the institutional aspect, the design of the programme, and/or the delivery of the programme. Furthermore, the review identifies political implications for research on oTPD—the institutional context including technical solutions, the general pedagogical approach, and educator support—and methodological limitations related to the ambiguity of the oTPD concepts and the transferability of case studies, which call for more research.