We have developed and validated a new pore-scale approach for the simulation of DC electrical resistivity measurements. The approach explicitly incorporates specific two-phase fluid distributions that are consistent with capillary pressure, saturation history, and percolation principles. Moreover, the simulation methodology properly reproduces pore-level fluid wettability, complex rock structure, and presence of conductive clay. We make use of a dynamic random-walk diffusion technique to simulate DC resistivity measurements via statistical averages of long-time diffusivity asymptotes. This strategy readily lends itself to accurately simulate the effects of explicit geometrical distributions of wetting films, pendular rings and snap-offs on DC resistivity measurements. We reproduce sequential drainage/imbibition cycles and their corresponding resistivity-index cycles for both water-wet and oil-wet generic clean rocks. To our knowledge, this has not been achieved by any previously published pore-scale simulation method. The simulation methodology introduced in this repot can therefore be used as a tool to assess the influence of wettability and saturation history for specific conditions of grain size distributions. Classical values of n within specific ranges (less than 2, about 2, about 3, and larger) are all justified making use of wettability arguments. Non-constant values of n through the complete saturation range can therefore be explained and even predicted for simple rocks when given their saturation history; conversely, their saturation history can be inferred from simulations of resistivity index performed with similar models.