Previously, we evaluated the impact of silver nanoparticles (Nano-Ag) on myogenesis-related gene expression during chicken embryogenesis, where the injection of 20 ppm of Nano-Ag resulted in gene expression alterations accompanied by hyperplasia of skeletal muscle fibers. We conducted the current study to furtherly investigate the effect of Nano-Ag on the post-hatch expression of myogenesis-related genes and its reflection on muscle development and productive performance of birds. Nano-Ag was administered in normal or magnetic water for 35 days. Productive performance parameters such as body weight (BW), body weight gain (BWG), feed intake (FI), feed conversion ratio (FCR), and European production efficiency factor (EPEF) were investigated. The expression of selected myogenesis-related genes was assessed at the mRNA and protein levels, and breast muscle development was also investigated. The results indicated no effect of Nano-Ag and magnetic water on BWG and FI. However, the group that was in ovo injected with 20 ppm Nano-Ag and got 20 ppm Nano-Ag in magnetic water had the lowest FCR, EPEF, and BW. In ovo injection of 40 ppm Nano-Ag followed by post-hatch administration of 40 ppm Nano-Ag in normal water increased the expression of myogenic determination factor 1 (MYOD1) mRNA and protein in breast muscles by 4.0 and 1.8 folds, respectively, and resulted in 19.9% more muscle fibers than the control group. The gene expression was raised at the mRNA level, but not at the protein level, when magnetic water was used alone and decreased the number of muscle fibers by 26.47% than the control group. Nano-Ag in combination with magnetic water is a committed growth-promoting agent in broiler production at a low dose.