Food processing has been gradually adopting the use of clean technologies that aim to minimize the generation of by-products. The use of winemaking by-products for the extraction of phenolic compounds is still incipient due to the lack of fast and efficient techniques. Thus, the aim of this study was to use the Microwave Hydrodiffusion and Gravity (MHG) technique to extract phenolic compounds from a winemaking by-product, the grape pomace (GP). The phenolic content of the extracts was analyzed by High Performance Liquid Chromatography (HPLC). Physicochemical and antioxidant properties were evaluated in the MHG extracts and in the GP before and after (co-product - CP) extraction. The GP had significant antioxidant properties and good yields in operating conditions of 2 W/g. Hydroxybenzoic acid, procyanidins, flavan-3-ols, and one flavanol were the phenolic compounds identified. The CP maintained the physicochemical and antioxidant properties similar to the GP. •Use of grape pomace (GP), winemaking by-product, as a source of phenolic compounds.•Phenolic extracts of GP were obtained by green technology.•The GP had antioxidant properties and good yields in operating conditions of 2 W/g.•The co-product showed satisfactory properties for its application in food products.•Microwave Hydrodiffusion and Gravity represents an efficient and clean technology.