The need for new retrofitting techniques is the consequence of an increasing interest in the conservation of historic construction. The global behavior of a stone masonry structure is often governed by the level of connection between masonry wall leaves and the overall quality of the masonry material. This paper presents the results of an investigation carried out on site and in the laboratory on multi-leaf stone masonry panels strengthened using stainless steel rod inserted in a grouted fabric sleeve. The aim is to increase the collaboration between weakly connected masonry leaves. Pull-out tests were conducted on site on full-scale stone masonry wall panels, with the aim of studying the force required to pull out a connector under uniaxial tension. Several wall panels were assembled in the laboratory using solid calcareous stones and weak mortar and the effectiveness of the connectors was tested in shear and compression on both virgin and damaged panels. The experimental tests allowed the analysis of the behavior of the multi-leaf panels. Experimental results show that a substantial improvement of the wall panels’ mechanical behavior can be achieved by applying transverse connectors.