OBJECTIVE The inflammatory cytokine interleukin-6 (IL-6) is associated with cardiovascular (CV) and kidney outcomes in various populations. However, data in patients with type 2 diabetes are limited. We assessed the association of IL-6 with CV and kidney outcomes in the Canagliflozin Cardiovascular Assessment Study (CANVAS) and determined the effect of canagliflozin on IL-6. RESEARCH DESIGN AND METHODS Patients with type 2 diabetes at high CV risk were randomly assigned to canagliflozin or placebo. Plasma IL-6 was measured at baseline and years 1, 3, and 6. The composite CV outcome was nonfatal myocardial infarction, nonfatal stroke, or CV death; the composite kidney outcome was sustained ≥40% estimated glomerular filtration rate decline, end-stage kidney disease, or kidney-related death. Multivariable-adjusted Cox proportional hazards regression was used to estimate the associations between IL-6 and the outcomes. The effect of canagliflozin on IL-6 over time was assessed with a repeated-measures mixed-effects model. RESULTS The geometric mean IL-6 at baseline, available in 3,503 (80.2%) participants, was 1.7 pg/mL. Each doubling of baseline IL-6 was associated with 14% (95% CI 4, 24) and 21% (95% CI 1, 45) increased risk of CV and kidney outcomes, respectively. Over 6 years, IL-6 increased by 5.8% (95% CI 3.4, 8.3) in the placebo group. Canagliflozin modestly attenuated the IL-6 increase (absolute percentage difference vs. placebo 4.4% [95% CI 1.3, 9.9; P = 0.01]). At year 1, each 25% lower level of IL-6 compared with baseline was associated with 7% (95% CI 1, 22) and 14% (95% CI 5, 22) lower risks for the CV and kidney outcome, respectively. CONCLUSIONS In patients with type 2 diabetes at high CV risk, baseline IL-6 and its 1-year change were associated with CV and kidney outcomes. The effect of IL-6–lowering therapy on CV, kidney, and safety outcomes remains to be tested.