Background <p>Diabetes mellitus represents a major global public health challenge, especially in middle-aged and older populations. The triglyceride-glucose A Body Shape Index (TyG-ABSI) composite index and inflammatory score are potential predictors of type 2 diabetes mellitus (T2DM). However, their independent and joint associations with incident T2DM in middle-aged and older Chinese adults remain unclear.</p> Methods <p>Data were obtained from the China Health and Retirement Longitudinal Study (CHARLS, 2011–2020), including 6,216 participants without diabetes at baseline. The TyG-ABSI index and inflammatory score (constructed from high-sensitivity C-reactive protein and white blood cell counts) were calculated. Multivariate Cox regression models, restricted cubic splines were used to evaluate their associations with incident T2DM.</p> Results <p>Higher TyG-ABSI and higher inflammatory score were independently associated with an increased T2DM risk (fully adjusted hazard ratio [HR]: 1.42, 95% confidence interval [CI]: 1.17–1.72 and 1.21, 95% CI: 1.02–1.44, respectively). Participants with concurrent high TyG-ABSI and high inflammatory score had a 69% higher T2DM risk (HR: 1.69, 95% CI: 1.30–2.21) than the reference group. Restricted cubic spline analyses showed approximately linear dose-response relationships. The combined index demonstrated superior discriminative ability (Harrell’s C-index) and significantly improved risk reclassification (NRI) and overall discrimination (IDI) compared with traditional risk factors alone.</p> Conclusion <p>TyG-ABSI composite index and inflammatory score were independently and jointly associated with incident T2DM in middle-aged and older Chinese adults. This combined application can improve T2DM risk stratification and facilitate early prevention.</p> Clinical trial number <p>Not applicable.</p>