Objective Although patients with rheumatoid arthritis (RA) experience fatigue, little is known about its causes and consequences, and a fully developed theoretical model explaining the experience of fatigue in RA is lacking. Our goal was to systematically review studies in RA that examined factors related to fatigue to gain more insight into its possible causes and consequences. Methods Medline, Web of Science, Scopus, and PsycINFO were searched for relevant studies. All studies with RA samples about the relationship between fatigue and other variables that defined dependent and independent variables and used multivariate statistical methods were preliminarily included. After reviewing 129 full texts, we identified 25 studies on possible causes of fatigue and 17 studies on possible consequences of fatigue. Results The studies found possible causes of fatigue in illness-related aspects, physical functioning, cognitive/emotional functioning, and social aspects. Additionally, being a woman was related to higher levels of fatigue. Inflammatory activity showed an unclear relationship with fatigue in RA. Possible consequences of fatigue were also found among illness-related aspects, physical functioning, cognitive/emotional functioning, and social aspects. The strongest evidence for a relationship between fatigue and other variables was found regarding pain, physical functioning, and depression. Conclusion This review summarizes the current knowledge in the field in order to inform future research on causes and consequences of fatigue in RA. However, the results are based on cross-sectional and longitudinal studies with different designs and different fatigue scales. For a better identification of causal associations between fatigue in RA and related factors, longitudinal prospective designs with adequate fatigue measurements are suggested.