Background Blackberry fruit processing results in biowaste in the form of blackberry fruit pomace (BFP), which retains many valuable biologically active compounds (BAM). Objective This study aimed to investigate the chemical constituents of BFP from Montenegro, as well as its antioxidant (a.a.) and antimicrobial (a.m.) activities against human oral flora and food isolates, depending on the extraction method used, either conventional maceration (MAC) or sonication/ultrasonically assisted extraction (UAE). Methods The phenolic profile and total phenol (TPC), flavonoid (TFC), anthocyanin (TAC), and proanthocyanidin (PC) contents were determined by HPLC and spectrophotometry. The a.a. was determined using the DPPH-based and FRAP methods, while the antimicrobial activity was analyzed using two appropriate assays. A battery of qualitative pharmacognosy tests was performed. The data were processed using principal component analysis (PCA). Results The most abundant secondary metabolite (SM) was ellagic acid (122.50/208.20 μg/mL) in both sample types. The UAE sample yielded a higher concentration of SM/BAM than the MAC sample, with the notable exceptions of quercetin and chlorogenic acid. The highest a.a. in the DPPH assay was measured as 1.27 μL/mL (IC 50 ) and 1045.45 μmol FRAP/L (in the FRAP assay). P. aeruginosa was the most sensitive strain (human pathogenic oral flora isolates) closely followed by S. aureus . B. cereus , among the food isolate microbes, was the most sensitive strain, requiring 3.125 mg/mL as the MIC of the UAE sample. Conclusion BFP is rich in phytochemicals with antioxidative and antimicrobial potential, whose concentration in extracts can be increased by sonication and possibly used as antioxidants and adjuvants in food, or novel antimicrobial agents for treatments in human oral cavity.