Objective: Negative body image is prevalent in women with rheumatoid arthritis and can affect other areas of well-being. Patients have expressed desire for body image to be addressed in treatment. Yet, it is not routinely addressed and no experimental intervention research has been conducted, until now. This randomized trial evaluated a brief online body image intervention for women with rheumatoid arthritis, with a focus on body functionality (everything the body is capable of doing) as the primary technique. Method: Women with rheumatoid arthritis and who wanted to feel better about their body (N = 84; Mage = 44.82) were randomized to the Expand Your Horizon intervention (comprising 3 writing exercises focusing on body functionality) or a waitlist control group. Primary outcomes concerned body image and secondary outcomes related to rheumatoid arthritis; these outcomes were assessed at pretest, posttest, and at 1-week and 1-month follow-up. Results: Multilevel modeling analyses showed that, relative to control, participants in the intervention experienced improvements in various aspects of body image (functionality appreciation, body appreciation, body satisfaction, body–self alienation) and decreases in depression, with effects persisting at 1-week and 1-month follow-up. No intervention effects were found for body–self harmony, rheumatoid arthritis-specific disability, pain-related disability, and anxiety. Conclusions: Focusing on body functionality can improve body image and reduce depression in women with rheumatoid arthritis. The intervention technique is easy and affordable to deliver and could be a fruitful addition to extant treatments for rheumatoid arthritis.