In this work, a new method based on reversed-phase high-performance liquid chromatography (HPLC) with fluorescence detection (FLD) was established for the determination of catechins and related oligomeric proanthocyanidins (PACs) in cranberry-based pharmaceuticals. Compounds were recovered by liquid extraction using methanol/water/hydrochloric acid (60:39:1, v:v:v) as the extraction solvent. The chromatographic separation was carried out using a core-shell C18 column under an elution program based on 0.1% formic acid in water and methanol as the components of the mobile phase. The flow rate was 0.4 mL min−1 and the injection volume was 5 μL. Chromatograms were acquired at 280 nm by UV–vis absorption and at λex 280 nm and λem 347 nm by fluorescence spectroscopy. Compared to UV detection, FLD demonstrated both increased sensitivity and selectivity to avoid interfering signals from other phenolic compounds present in the samples. Data resulting from the analysis of cranberry-based products was exploited to tackle an exploratory characterization and classification using principal component analysis. Samples were clustered according to their compositions and those enriched with PACs with antibacterial activity were clearly distinguished from the others.