The growing thermal demands of modern energy conversion, chemical processing, and micro-scale electronic devices necessitate advanced heat and mass transfer strategies, particularly for smart fluids operating in reactive environments. In this work, the flow behavior of an electrically conducting Oldroyd-B nanofluid containing motile microorganisms is analyzed within the Cattaneo-Christov double-diffusion (CCDD) paradigm, which accounts for finite thermal and solutal relaxation times beyond the classical Fourier-Fick theory. The model incorporates mixed convection, and Arrhenius-type chemical reactions to capture complex transport interactions. By employing the Chebyshev Collocation Method (CCM), the coupled nonlinear ordinary differential equations governing the system are solved with high spectral accuracy. The parametric analysis reveals that buoyancy-induced forces significantly strengthen convective transport. Distinct and contrasting influences of relaxation and retardation parameters are observed in the velocity field, highlighting the viscoelastic nature of the fluid. Moreover, thermophoresis and Dufour mechanisms promote thermal and concentration diffusion, while increasing Prandtl and Schmidt numbers, thermal relaxation time, and chemical reaction rate diminish the associated boundary layers. The combined effects of non-Fourier diffusion, and chemical activity lead to transport characteristics unattainable under classical assumptions. These findings offer valuable physical insight for the design and optimization of nanofluid-based thermal systems in advanced industrial and technological applications.
