The objective of this research was to develop an economical, structurally effective, and practically applicable steel fiber reinforced mortar (SFRM) which could be applied onto the hollow brick infills of a reinforced concrete (RC) structure. Masonry walls were almost converted into strong and rigid infills with the application of SFRM. Two different mix proportions were produced with the composition of Portland cement, fine aggregate, water, and plasticizer or bonding agent as the chemical admixture. Tests were carried out to determine the optimum steel fiber content (1%, 2%, or 4% by volume) and to clarify the use of plasticizer or bonding agent in the mortar in the context of sticking ability, flexural, compressive, and adhesion strengths. As a result, mortar with plasticizer and 2% steel fiber (by volume) came out to be the optimum mortar mixture as strengthening material. The performance of RC frame strengthened with SFRM containing plasticizer and 2% steel fiber by volume was compared to those of the hollow brick infilled RC frame without strengthened mortar and the hollow brick infilled RC frame with reference mortar. It was observed that the specimen strengthened with the optimum mortar mix satisfied the target objectives of this study.