Hypericum perforatum L., commonly known as St. John’s wort, is one of the medicinal plants that have been used for centuries in several European countries to cure skin wounds, burns, and neuralgia. It is additionally used as a dietary supplement. The most of bioactive compounds in H. perforatum are polyphenols and flavonoids. Due to the rising demand for new antibiotic compounds, recent laboratory studies have determined the antioxidant, antifungal, antibacterial, and cytotoxic activities of H. perforatum extracts. Currently, field-grown plant material is often used in medicine, although the quality of these products is strongly impacted by biological and environmental factors. Alternatively, adventitious root cultures provide a manufacturing platform unaffected by environmental influences and provide a uniform supply of standard extract and bioactive compounds. Bioreactor cultures are commonly used in the production of medicinal products for industry. This chapter examines the research findings from the bioreactor culture technology of H. perforatum for the production of root biomass and bioactive compounds like phenolics and flavonoids, especially chlorogenic acid, and quercetin.