Stability of disease resistance is critical in maize breeding because genotype × environment interaction (GEI) can substantially influence trait expression. In the present study, 31 multi-parent advanced generation intercross (MAGIC) recombinant inbred lines (RILs), along with 2 checks, were evaluated for northern corn leaf blight (NCLB) across 3 locations, while 32 RILs were assessed for their reaction to sorghum downy mildew (SDM) across 3 rainy seasons. Pooled analysis of variance (ANOVA) revealed a non-significant GEI for SDM, indicating stable genotype performance across seasons, whereas NCLB showed significant GEI. Correlation analysis further supported these results: SDM exhibited very high inter-season correlations, suggesting minimal genotype re-ranking, while NCLB showed moderate to low correlations among environments, reflecting environmental divergence and crossover interactions. Unweighted pair group method with arithmetic mean (UPGMA) clustering grouped the genotypes into three major clusters for both diseases but did not distinctly separate resistant and susceptible classes, suggesting quantitative inheritance and continuous phenotypic variation. Further stability analysis using additive main effects and multiplicative interaction (AMMI) and genotype plus genotype-by-environment interaction (GGE) biplot models identified G13, G15 and G2 as stable and resistant for NCLB, while G15, G10, G16 and G32 exhibited broad adaptation across environments. These stable MAGIC RILs for NCLB disease represent valuable genetic resources for breeding durable resistance in NCLB prone maize production regions.