<p>This research article presents a detailed analysis of nonlinear thermal radiation effects in the bioconvective flow of a micropolar nanofluid containing gyrotactic microorganisms over an oscillating curved surface. The formulation accounts for microstructural fluid behavior, Brownian motion, thermophoresis, and microorganism-induced bioconvection, providing a comprehensive framework for understanding transport phenomena in complex fluids. The governing partial differential equations are formulated using a curvilinear coordinate system to accurately capture the influence of surface curvature and oscillation. Nonlinear thermal radiation is incorporated into the energy equation to model realistic radiative heat transfer in high-temperature environments. The coupled system of equations governing momentum, angular momentum, energy, nanoparticle concentration, and microorganism density is reduced to a set of nonlinear ordinary differential equations via similarity transformations. The Homotopy Analysis Method (HAM) is employed to derive analytical solutions, offering adjustable convergence control and high accuracy. Graphical analysis reveals that the microorganism concentration profile decreases with increasing values of the Peclet number, microorganism difference parameter, bioconvection Lewis number, and curvature parameter. Conversely, the local motile density number increases with all the aforementioned parameters. From the tabulated data, it is noticed that the local Nusselt Number magnitude inclines up to 8% with developing values of the dimensionless ratio parameter, while for the Brownian parameter, the y Nusselt number magnitude drops bapproximately 0.05%. The magnitude of the local Motile density number grows up to 1.2% and 5.7% against the microorganism difference parameter and Peclet number, respectively. These findings enhance the understanding of microscale fluid dynamics and have promising applications in bio-microsystems, thermal regulation, and nanotechnology-based fluid processing.</p>