Fresh chicken meat is a very perishable good, even at refrigerated storage conditions, due to psychrophilic microbial growth and physicochemical changes. The present study focuses on the use of rosemary (Rosmarinus officinalis L.) essential oil (REO), supercritical CO2 processing and their synergism to increase the microbial inactivation in chicken breast meat. E. coli and L. innocua were inoculated on the chicken breast surface, and the inactivation effects of two different processes, namely SC-CO2 and SC-MAPCO2, were compared with or without the addition of REO. Moreover, the impact of the treatments on the superficial color of the meat was considered. The study demonstrated a synergic effect with 1% REO and supercritical CO2 for the inactivation of E. coli on chicken meat, while for L. innocua, there was no synergism. Regarding SC-CO2 treatment, the E. coli reduction was 1.29 and 3.31 log CFU/g, while for L. innocua, it was 1.42 and 1.11 log CFU/g, respectively, without and with the addition of 1.0% of REO. The same amount of REO allowed us to obtain a reduction of 1.3 log CFU/g of E. coli when coupled with SC-MAPCO2. For L. innocua, no reduction was obtained, either with SC-MAPCO2 or together with REO. The synergism of SC-MAPCO2 with 1% REO was confirmed for the total psychrophilic bacteria, demonstrating a strong dependence on the microorganism. The color modification induced by the SC-MAPCO2 process was lower than the SC-CO2 treatment. Overall, this study demonstrated a possible synergism of the technologies which can support the development of innovative methods to improve the safety and shelf-life of chicken breast meat.