In recent years, macroalgae have gained relevance as a new source of active compounds with potential use in the food industry. However, Ecklonia cava is currently the only macroalga approved by the European Food Safety Authority (EFSA) as a source of phlorotannins for novel foods, specifically, an ethanolic extract marketed as SeaPolynol™. Other brown algae species contain phlorotannins and have demonstrated various biological activities, including antioxidant, anti-inflammatory, and antidiabetic effects. However, these species have not been authorized by the EFSA as novel foods, and deeper knowledge of their composition, concentration, and safety is needed. This study aimed to optimize the extraction of phlorotannins via pressurized liquid extraction (PLE) in two brown macroalgae, Pelvetia canaliculata and Laminaria ochroleuca. The experiments were designed using response surface methodology (RSM), and the independent variables were set at the following ranges: time (t, 1–25 min), temperature (T, 50–200°C), and solvent concentration (S, 0–100% ethanol). Phlorotannins were identified and quantified via HPLC-ESI-QqQ-MS/MS. In total, 45 phlorotannins were identified, highlighting their content in difucol, deshydroxyhexafuhalol, and eckstolonol, and in higher concentration for L. ochroleuca (176.3 mg/g extract, E) compared to P. canaliculata (81.4 mg/g E). Generally, the extraction system prefers short times, mild temperatures, and a high percentage of ethanol. This study contributes to a deeper understanding of the phlorotannins present in brown macroalgae and highlights L. ochroleuca as a promising source for the development of novel food ingredients with potential health benefits.