Valorising green waste will greatly enhance and promote the sustainable management of this large volume resource. One potential way to achieve this is the extraction of high value human health promoting chemicals (e.g., polyphenols) from this material. Our primary aim was to identify the main polyphenols present in four contrasting green waste feedstocks, namely Smyrnium olusatrum, Urtica dioica, Allium ursinum and Ulex europaeus, using UPLC-HDMSE. Polyphenol-rich Camellia sinensis (green tea) was used as a reference material. Samples were extracted and analysed by UPLC-HDMSE, which was followed by data processing using Progenesis QI and EZ Info. A total of 77 high scoring polyphenolic compounds with reported benefits to human health were tentatively identified in the samples, with abundances varying across the plant types; A. ursinum was seen to be the least abundant in respect to the polyphenols identified, whereas U. europaeus was the most abundant. Important components with a diverse range of bioactivity, such as procyanidins, (−)-epigallocatechin, naringenin, eriodictyol and iso-liquiritigenin, were observed, plus a number of phytoestrogens such as daidzein, glycitin and genistein. This research provides a route to valorise green waste through the creation of nutritional supplements which may aid in the prevention of disease.