In the present article, we analyze hydrodynamically fully developed flow (FDF) actuated by electric field and pressure gradient (PG) in a microchannel consisting of parallel plates using analytical methods. The dimensionless velocity field is obtained after solving the momentum equation and subsequently the volumetric flow rate in dimensionless form is derived. The prime motivation of the current investigation is to calculate the flow rate sensitivity on the Debye–Hückel parameter (k) along with the zeta potential, respectively. The flow rate variation rate with regard to k enhances along with the zeta potential and such increment further augments for thicker electrical double layer (EDL). Also, the rate of change of volumetric flow rate with regard to the zeta potential rises with k for its lower values and becomes practically invariant for larger values of k. Moreover, the relative percentage deviation in the volumetric flow rate of the mixed pressure and electric field driven flow from that of the purely electroosmotic flow decreases with the reduction in the thickness of the EDL, whereas the relative percentage deviation increases drastically with the decrement in zeta potential.