BACKGROUND: Heart failure (HF) in patients with type 2 diabetes mellitus (T2D) has received growing attention. We examined the effect of HF development on prognosis compared with other cardiovascular or renal diagnoses in patients with T2D. METHODS AND RESULTS: Patients with new T2D diagnosis patients were identified between 1998 and 2015 through Danish nationwide registers. At yearly landmark timepoints after T2D diagnosis, we estimated the 5-year risks of death, 5-year risk ratios, and decrease in lifespan within 5 years associated with the development of HF, ischemic heart disease, stroke, peripheral artery disease, and chronic kidney disease. A total of 153 403 patients with newly diagnosed T2D were followed for a median of 9.7 years (interquartile range, 5.8-13.9) during which 48 087 patients died. The 5-year risk ratio of death associated with HF development 5 years after T2D diagnosis was 3 times higher (CI, 2.9-3.1) than patients free of diagnoses (CI, 2.9-3.1). Five-year risk ratios were lower for ischemic heart disease (1.3 [1.3-1.4]), stroke (2.2 [2.1-2.2]), chronic kidney disease (1.7 [1.7-1.8]), and peripheral artery disease (2.3 [2.3-2.4]). The corresponding decrease in lifespan within 5 years when compared with patients free of diagnoses (in months) was HF 11.7 (11.6-11.8), ischemic heart disease 1.6 (1.5-1.7), stroke 6.4 (6.3-6.5), chronic kidney disease 4.4 (4.3-4.6), and peripheral artery disease 6.9 (6.8-7.0). HF in combination with any other diagnosis imposed the greatest risk of death and decrease in life span compared with other combinations. Supplemental analysis led to similar results when stratified according to age, sex, and comorbidity status, and inclusion period. CONCLUSIONS: HF development, at any year since T2D diagnosis, was associated with the highest 5-year absolute and relative risk of death, and decrease in lifespan within 5 years, when compared with development of other cardiovascular or renal diagnoses.