Subcritical water extraction (SWE) is a high-efficiency and environmentally sustainable technique for extracting bioactive compounds from red ginseng marc (RGM). In this study, CO2 was introduced into the SWE system as a green catalyst to enhance the extraction efficiency of biologically active compounds from RGM. A wide range of parameters, such as temperature (140–180 °C), pressure (10–20 MPa), and time (10–60 min), were optimized using response surface methodology to maximize the recovery of highly valuable bioactive components, including rare ginsenosides (RGs), total phenolic contents (TPCs), and Maillard reaction products (MRPs), as well as the antioxidant activity of the RGM extract. The extract obtained using CO2-assisted SWE (CO2-SWE) under the optimal conditions (172 °C, 10 MPa, and 10 min) was enriched in RGs (1.02–2.16 times), TPCs (0.98–4.68 times), and MRPs (1.08–2.20 times) and exhibited enhanced antioxidant activities (1.07–3.50 times) compared with the extracts produced by conventional SWE (N2 environment) and Soxhlet extraction with H2O or 80 vol% ethanol. Thus, CO2-SWE is an environmentally friendly and nontoxic technique with considerable potential for use in the pharmaceutical, cosmeceutical, and functional food sectors.