The forced convective boundary layer flow of viscous incompressible time-dependent fluid containing water-based nanofluids and gyrotactic microorganisms simultaneously, from a flat surface with leading edge accretion (or ablation), is theoretically investigated in the present study. In doing so, the governing conservation equations are rendered into a nonlinear system of ordinary differential equations by means of utilizing appropriate coordinates transformations. MAPLE symbolic software is employed to solve these equations, which are subjected to impose boundary conditions using the Runge–Kutta–Fehlberg fourth-fifth order numerical method. It is noteworthy that the results of the present study are in an excellent agreement with previous solutions available in literature. The effect of selected parameters on velocity, temperature, nanoparticle volume fraction and motile microorganism density function is then investigated. Tabular solutions are included for the skin friction, heat transfer rate, nano-particle mass transfer rate and microorganism transfer rate. Applications of the study arise in advanced micro-flow devices to bio-modified nanomaterials processing.