The electrical resistance sensor is an appropriate and inexpensive tool for measuring soil matric potential (ψ). These sensors are widely used in irrigation agriculture. One drawback of the resistance sensors, however, is that the measurements often are not accurate across a wide range of moisture conditions. The objective of this study was to design a resistance sensor that can measure accurately and precisely across a wide range of moisture conditions, thereby extending the measurement capabilities of currently available sensors. The sensor consists of two electrodes embedded in a sand–plaster matrix that is stabilized with polyacrylamide. The sensor was calibrated and tested to determine its sensitivity to soil texture, temperature, and electrical conductivity. Experimental results showed that the sensor was able to determine matric potentials in the range of −7.5 kPa to −10 MPa, and showed excellent precision, with a RMSE <5 kPa across the range of −5 to −80 kPa. A standard electrical resistance–water potential curve can be established in the laboratory on a soil, and can then be applied to different soil types.