This paper investigates the collective impacts of magnetic field, Brownian diffusion, thermophoresis, and buoyancy force on the Casson – Williamson nanoliquid over a rough slender cylinder. The novelty of this paper is to inspect the effect of inclined magnetic field (in particular, at an angle of 45 0 to the liquid flow) over an oxytactic bioconvective nanoliquid flow. To simulate the problem, a set of nonlinearly coupled partial differential equations is employed, and nonsimilar transformations are used to reduce them into nondimensional form. For mathematical simplification, an implicit finite difference scheme and Quasilinearization technique are used. The outcomes for the influences of several significant parameters on the mass and heat transmission properties are illustrated through graphs. Temperature and velocity profiles are pronounced to be more for augmenting values of thermophoresis and Brownian motion parameters. The heat transmission and coefficient of skin friction are enhanced with the surface roughness parameter, while skin friction increases and the heat transmission decreases with the magnetic parameter. The mass transmission rate of oxygen liquid, and microbial density number enhance with the higher bioconvection Lewis number and Peclet number. In a comparison with earlier published works, the results are discovered to be highly concordant.