<p>Casson nanofluids exhibit superior thermal performance, enabling various industrial and engineering applications. Understanding their flow and heat transfer is essential for efficient thermal system design. This study analyzes the steady magnetohydrodynamic (MHD) boundary layer flow of a Casson nanofluid over a stretching cylinder, incorporating Joule heating and the Cattaneo–Christov heat flux model. Thermophoresis and Brownian motion effects are included in the energy and concentration equations, and convective boundary conditions are applied. The governing partial differential equations are transformed into ordinary differential equations using similarity transformations and solved analytically via Mathematica using the Homotopy Analysis Method (HAM). This study presents a novel analysis of magnetohydrodynamic Casson nanofluid flow over a stretching cylinder, incorporating non-Fourier heat flux, nanoparticle transport, and Joule heating simultaneously, with convective boundary conditions to capture realistic industrial thermal behavior. The impact of dimensionless parameters, including the Casson parameter, curvature, porosity, charge influence, Prandtl number, Schmidt number, thermophoresis, Brownian motion, Biot numbers, and radiation, is examined. Velocity, temperature, and concentration profiles, along with skin friction, Nusselt number, and Sherwood number, are presented graphically and in tables. Significant variations in flow, heat, and mass transfer characteristics are observed. The findings provide a comprehensive understanding of Casson nanofluid behavior over stretching cylinders, offering insights for the design of efficient thermal systems in industrial and engineering applications, where non-Fourier heat conduction and nanoparticle transport are significant.</p>