This study investigates double‐diffusive transport and entropy generation in a wavy cylindrical enclosure containing Cu─H₂O Casson nanofluid under magnetic field and thermal radiation effects. The governing equations were solved numerically using the finite element method with Galerkin formulation. The investigation covered parametric ranges including Rayleigh number (10³ ≤ Ra ≤ 10⁶), Hartmann number (0 ≤ Ha ≤ 40), magnetic field inclination (0° ≤ γ ≤ 90°), nanoparticle volume fraction (0 ≤ φ ≤ 0.15), Casson parameter (0.1 ≤ η ≤ 1), radiation parameter (0 ≤ Rd ≤ 4), thermal conductivity parameter (0 ≤ λ ≤ 4), Lewis number (0.5 ≤ Le ≤ 5), and buoyancy ratio (0.25 ≤ Nz ≤ 1.5). Results demonstrated that increasing Ra from 10³ to 10⁶ enhanced heat transfer by 60%, while increasing Ha to 40 reduced fluid circulation by 75%. The Casson parameter significantly influenced flow characteristics, with stream function values increasing by 75% as η approached Newtonian behavior. Thermal radiation parameters jointly moderated temperature gradients, with Rd causing a 15%–20% reduction in thermal stratification. The Lewis number and buoyancy ratio showed strong coupled effects, with the Sherwood number increasing by 150% as Le increased from 0.5 to 5. These findings have practical applications in advanced heat exchanger design, thermal energy storage systems, electronic cooling technologies, and biomedical devices, where controlled heat and mass transfer of non‐Newtonian fluids is crucial.