The calculation of electro-dipping force, acting on a dielectric particle, attached to the boundary between water and nonpolar fluid, is important for the characterization of the surface charge density of micron-size objects and their three-phase contact angles. The problem was solved semi-analytically, using the Mahler–Fox transformation in the simplified case of one phase with infinite dielectric permittivity. We generalize this approach, taking into consideration the finite dielectric permittivity of the polar phase. We propose a numerical method for calculating the distribution of the electrostatic potential in all phases and the respective values of the dimensionless electro-dipping force. The expression for the weak singularity parameter at the three-phase contact line is analytically derived. In all studied cases, it is weaker than that in the model case. The obtained results show that: (i) the electrostatic potential distribution is close to that in the model case for micron-size particles, large values of the ionic strength and dielectric constant of the polar phase; (ii) the force, arising from the electrostatic field in the polar phase, cannot be neglected for small (nano-size) particles and low ionic strengths.