The numerous applications of non-Newtonian nanofluids in engineering, geothermal and industrial processes motivated us to formulate a comprehensive model for unsteady 3D flow of an Oldroyd-B nanomaterial. Brownian motion and thermophoresis characteristics are also accommodated through a Buongiorno nanofluid model. Moreover, assessments of thermal stratification, chemical reaction, solutal stratification, mixed convection, and prescribed heat source are also elucidated in the combinations of momentum, energy, and concentration equations. The transformed system of ODEs is tackled by homotopy analysis method. A comparison benchmark for limited cases is also constructed to confirm the correctness of whole parametric exploration. It is scrutinized through present communication that intensifying values of Prandtl factor, unsteady factor, heat distribution indices, thermal stratification constraint, mixed convective parameter, and Deborah number for time retardation diminish the temperature of the nanomaterial. Also, escalating amounts of Lewis number, chemically reactive species, Brownian motion parameter, and solutal stratification constraint reduce the concentration profile.