Aims: Type 2 diabetes (T2D) and heart failure (HF) frequently coexist, but whether clinical outcomes and treatment effects of sodium–glucose cotransporter 2 inhibitors (SGLT2i) vary in relation to background glucose-lowering therapy (GLT) in this population is uncertain. Methods and results: DELIVER randomized patients with HF and left ventricular ejection fraction (LVEF) >40% to dapagliflozin or placebo. The primary outcome was a composite of worsening HF (HF hospitalization or urgent HF visit) or cardiovascular death. In this pre-specified analysis of participants with T2D, treatment effects were assessed by number and class of background GLT(s). Of 3150 participants with T2D at baseline, 22.9% were on no GLT, 36.5% were treated with 1 GLT, and 40.6% with ≥2 GLTs. During follow-up (median: 2.3 years), treatment benefits of dapagliflozin (vs. placebo) on the primary outcome were consistent irrespective of the number of background GLTs (0 GLTs: hazard ratio [HR] 0.71, 95% confidence interval [CI] 0.50–1.00; 1 GLT: HR 1.04, 95% CI 0.80–1.34; ≥2 GLTs: HR 0.71, 95% CI 0.56–0.90; p_interaction = 0.59). Similar findings were observed among participants with (HR 0.73, 95% CI 0.59–0.92) and without background metformin use (HR 0.89, 95% CI 0.72–1.11; p_interaction = 0.22) and in participants with (HR 0.89, 95% CI 0.69–1.16) and without background insulin use (HR 0.78, 95% CI 0.65–0.95; p_interaction = 0.45). Dapagliflozin was well-tolerated irrespective of the number of background GLTs. Conclusions: Dapagliflozin safely and consistently improved clinical outcomes among individuals with T2D and HF with LVEF >40% irrespective of the number and class of background GLTs, and the benefits were not influenced by concomitant metformin or insulin use. These data bolster contemporary guidelines supporting first-line SGLT2i among individuals with T2D and HF, irrespective of background GLT.