Masonry infill piers are panel segments between openings and Reinforced Concrete (RC) columns. Reconnaissance experience shows that piers are significant structural members in low-rise RC buildings. A simulation of the seismic behavior of masonry infill piers should be included in seismic evaluation. This paper reports a simplified assessment model of masonry infill piers. The proposed model establishes a triple linear curve to describe a load deformation envelope curve for masonry infill piers. The stiffness of the triple linear curve is calculated in accordance with ASCE/SEI 41-13. The ultimate lateral strength of the infill piers is estimated by bed-joint sliding shear, the splitting strength of vertical (head) joints, and the splitting strength of bricks. These sources of strength are determined by the major fracture path of the infill piers. The residual strength and ultimate deformation of the infill piers are also reported in this paper. In addition, to verify the proposed assessment model, three cyclic loading tests of full-scale RC columns with masonry infill piers are reported. These masonry panels were 900 mm in length, 2700 mm in height, and 200 mm in thickness and made of 200 mm × 95 mm × 53 mm solid clay bricks. Identical RC column sections with a depth of 300 mm and a width of 400 mm were used in all the specimens. Analytical results show that the calculated stiffness is similar to the test results. Therefore, the calculated ultimate strength is conservative without a loss of accuracy. However, the prediction of residual strength and ultimate deformation is conservative.