Many middle-aged or older women are treated for cancer and their quality of life can be significantly impaired following treatment. Exercise and dietary interventions could address this. The aim of this review was to determine whether exercise and/or dietary interventions which are scaffolded by behaviour change theories and techniques are associated with improved quality of life in middle-aged and older women following cancer treatment. Secondary outcomes included self-efficacy, distress, waist circumference, and food variety. A search of CINAHL (EBSCOhost), Embase, MEDLINE (EBSCOhost), PsycINFO, PubMed and Scopus databases up to 17th November 2022 was conducted. A narrative summary was provided. Twenty articles discussing 18 independent randomised controlled trials/interventions were included, with a total of 1754 participants. No studies reported the outcomes of distress or food variety. Exercise and/or dietary interventions had mixed effects on quality of life, self-efficacy and waist circumference (positive effect: n = 4/14; n = 3/5; n = 4/7, respectively). Two-thirds of the interventions (exercise-only, n = 2; exercise and diet, n = 2) that demonstrated an improvement in quality-of-life scores were based upon Social Cognitive Theory. All studies that reported improvements in waist circumference employed combined exercise and dietary interventions, with individualised aspects for the dietary components. Exercise and/or dietary interventions could potentially enhance quality of life and self-efficacy, and reduce waist circumference, in middle-aged and older women treated for cancer. Although findings are currently mixed, avenues for the development of interventions include ensuring there is a theoretical underpinning and incorporating more behaviour change techniques in exercise and/or dietary interventions in this population.