<p>Spent tea leaves (STLs) represent an industrial waste for both the foods and beverages industry, despite their potential as a source of bioactive compounds. The optimization of extraction parameters for target bioactive molecules from STLs has already been investigated, while the brewing process has never been considered in the bioactive compounds’ recovery. This study evaluates how the combination of different brewing systems (Pure Brew, French Press and Gaiwan) and extraction methods and technologies (conventional solid–liquid extraction with water and with ethanol, ultrasound- and microwave-assisted extraction and supercritical fluid extraction) could affect the antioxidant profile of extracts obtained from black spent tea (Twinings and Black Assam tea). Spectrophotometric and chromatographic analyses showed that ultrasound extraction yielded the highest polyphenol content (around 20% more than ethanolic extracts) and efficiently recovered key phenolic acids and flavanols. Brewing systems significantly influenced extractability of phenolic compounds, with Pure Brew being optimal for Twinings and Gaiwan for Black Assam. By optimizing the combination of brewing and extraction methods, sustainable waste management practices and the valorisation of food industry byproducts could be improved.</p>