Aims: Two fixed-ratio combinations (FRCs) of basal insulin and glucagon-like peptide-1 receptor agonist (GLP-1RA) are available for once-daily use in adults with type 2 diabetes. We aimed to review the clinical evidence for the efficacy and safety of changing treatment from a basal–bolus insulin (BBI) regimen or a premix insulin to these combination treatments (fixed-ratio or loose) and provide expert opinion on the practicalities of making such a change. Methods: Relevant clinical and trial evidence and general review articles were identified through a literature review of ProQuest (comprising BIOSIS Previews®, Current Contents® Search, Embase® and MEDLINE®) for articles published between 2009 and 2021. Results: We identified nine articles reporting the results of FRCs, and seven articles reporting results of loose combinations of basal insulin and GLP-1RAs, in people who transitioned treatment from BBI or premix regimens. In most trials, combination treatment led to improved or equivalent glycaemic control, and a reduction in body weight or BMI, versus the original regimens. Some trials reported a reduction in total insulin dose. A few trials reported reduced or unchanged hypoglycaemia rates, or increased patient satisfaction, with combination therapy where these endpoints were examined. We provide guidance on transitioning of treatment and the patient types most likely to benefit. Conclusions: In people not achieving glycaemic control with BBI or premix insulin regimens, an FRC or loose combination of basal insulin and GLP-1RA may improve control, decrease the risk of body weight gain or hypoglycaemia and reduce the complexity of treatment.