To investigate the effect of physical activity (PA) (both general and its type) on self-esteem during and after cancer treatment. A systematic search was conducted across PubMed, Web of Science, Scopus, SPORTDiscuss, and PsycINFO from their inception to February 2024. The systematic review included 32 studies, with 15 studies (13 RCT and 2 quasi-experimental) and 3604 participants (66.7% female) included in the meta-analysis involving controlled trials using a control group and at least one PA intervention group. The study was registered in PROSPERO (CRD42022309771). Risk of bias for RCTs was assessed using the Cochrane Collaboration's tool for assessing risk of bias (RoB2), and quasi-experimental studies with the Joanna Briggs Institute critical appraisal tool. PA significantly improved self-esteem during and after cancer treatment (pooled SMD = 0.32, p < 0.01). Specifically, aerobic PA (pooled SMD = 0.33, p = 0.04) and mind-body exercise (pooled SMD = 0.70, p = 0.03) had positive effects on self-esteem. Overall, PA interventions improved self-esteem during cancer treatment (pooled SMD = 0.50, p = 0.01) and in PA interventions lasting more than 12 weeks (pooled SMD = 0.44, p = 0.02). In conclusion, PA (specifically, aerobic and mind-body exercises) may have a positive effect on self-esteem during and after cancer treatment, with cancer status and the duration of the intervention being key factors.