BackgroundThis study aimed to examine the association between the incident onset of T2DM and 5- and 10-year risks of CVD and HF in people with IGT identified in primary care in South and West Auckland, New Zealand (NZ) between 1994 and 2019.MethodsWe compared CVD and HF risks in patients with IGT and with/without T2D newly diagnosed within the exposure window (1–5 years). Tapered matching and landmark analysis (to account for immortal bias) were used to control for potential effects of known confounders.ResultsAmong 26,794 patients enrolled with IGT, 845 had T2D newly diagnosed within 5 years from enrolment (landmark date) and 15,452 did not have T2D diagnosed. Patients progressing to T2D (vs. those not progressing) had a similar 5-year risk for CVD (hazard ratio 1.19; 95% CI 0.61–2.32) but significantly higher 10-year risk of CVD (2.45(1.40–4.29)), 5-year risk of HF (1.94(1.20–3.12)) and 10-year risk of HF (2.84(1.83–4.39). The association between the onset of T2D and risk of 10-year risk of CVD, 5-year and 10-year risk of HF was more likely among men, the socioeconomically deprived, those currently smoking, patients with higher metabolic measures and/or those with lower renal function. Patients of NZ European ethnicity had a lower 10-year risk of CVD.ConclusionsThe study suggests that the diagnosis of T2D mediates the risk of CVD and HF in people with IGT. The development of risk scores to identify and better manage individuals with IGT at high risk of T2D is warranted.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12933-023-01871-y.