The present work studies the effects of a commercial starter culture (L. plantarum Lyoflora V3, Sacco) on microbiological and chemical parameters during fermentation of Aitana and Caiazzana black olives and Nocellara del Belice turning colour olives. Total phenol content and carpological parameters were assessed on raw olives, while pH, free acidity and different single phenols of brine samples were analysed. The two black olive cultivars were ready to eat after two months while Nocellara del Belice after five months. Different microbial populations were assessed throughout the brining period. E. coli was never detected in all the analysed samples, while S. aureus was detected (2.23 Log10 CFU mL−1) only at beginning of fermentation in Nocellara del Belice control sample. Both hydroxytyrosol and tyrosol trends depended on starter, cultivar and time of fermentation, while oleuropein and verbascoside showed a different behaviour among cultivars. The starter addition has resulted in faster acidification, but a low pH value (3.39 min and 3.71 max values in the final products) was reached in both inoculated and control samples of the three cultivars. According to the Principal Component Analysis, hardness, bitter and acid parameters had an incisive role in the explanation of the variability among the sensory data of the three cultivars. The sensory profiles evaluated at the end of fermentation highlighted significant differences among the samples of the three cultivars for all descriptors.