Aims: To assess the relationship of longitudinal changes in fat mass (FM), lean mass (LM) and waist circumference (WC) with incident kidney outcomes in people with overweight/obesity and type 2 diabetes mellitus (T2DM). Materials and methods: A total of 3927 participants with baseline estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m2 from the Look AHEAD (Action for Health in Diabetes) trial were included. The primary outcome was kidney outcomes, defined as a decrease in eGFR of at least 40% from baseline at follow-up visit, or end-stage kidney disease. Results: During a median follow-up of 8.0 years, 450 kidney outcomes were documented after the first 1 year. In the intensive lifestyle intervention (ILI) group, reductions in FM (per 10% decrease, adjusted hazard ratio [HR] 0.80, 95% confidence interval [CI] 0.69-0.94) and WC (per 10% decrease, adjusted HR 0.72, 95% CI 0.59-0.88) from baseline to 1-year follow-up were significantly associated with a lower risk of kidney outcomes. The change in LM was not significantly associated with risk of kidney outcomes (per 10% decrease, adjusted HR 0.78, 95% CI 0.58-1.06). In the diabetes support and education group (control group), no significant association was found between changes in body composition and kidney outcomes. Similar results were observed for the 4-year changes in body composition. Conclusions: In this post hoc analysis of the Look AHEAD trial, longitudinal declines in FM and WC were associated with a lower risk of kidney outcomes in the ILI group in participants with overweight/obesity and T2DM.