To evaluate the effectiveness and safety profile of switching to insulin glargine 300 U/mL (Gla-U300) in patients with uncontrolled type 2 diabetes (T2D) on basal insulin in Saudi Arabia. We conducted a multicentre retrospective study that retrieved the medical records of adult T2D patients switched to Gla-U300 because of poor glycaemic control on their basal insulin. Data covering 6 months ± 30 days before and after the switch were retrieved. Data from 718 patients were analysed. The mean HbA1c decreased significantly 6 months after switching to Gla-U300, with a mean reduction of 0.7% (95% confidence interval [CI] 0.6%-0.9%; P < .001). The percentage of patients with HbA1c levels of less than 7% increased from 6.4% before switching to 10.3% after switching to Gla-U300. The percentage of patients achieving the predefined individualized HbA1c goal increased from 8.6% before switching to 17.3% after switching to Gla-U300. The mean daily insulin dose decreased from a baseline level of 32.2 (± 14.7) to 31.0 (± 15) U (P = .09). About 36.1 of the patients required adjustment to the initial dose. Gla-300 was well tolerated; 4.5% of the patients experienced overall confirmed or symptomatic hypoglycaemia, compared with 15.3% before switching to Gla-U300. The incidence of severe hypoglycaemia after switching was 0.6% (n = 4 patients), compared with 1% before switching. Real-world evidence supports the effectiveness of switching to Gla-U300 from first-generation basal insulin in T2D in Saudi Arabia.