Given the need to ensure sustainable development in agriculture, waste should be managed properly. This also applies to manure from the breeding of non-conventional animal species. A study was conducted on the vermicomposting of fallow deer (Dama dama) manure using Eisenia fetida Sav. earthworms. The study assessed the effect of adding cellulose from cardboard and decomposed hay on the properties of the resulting vermicompost. In the study, clean fallow deer manure (FDM), fallow deer manure mixed with cardboard (FDMC) in a 1:1 ratio, and fallow deer manure mixed with decomposed hay (FDMH) in a 1:1 ratio were processed. The basic physicochemical properties of the waste materials and vermicomposts were evaluated, as well as the population dynamics of compost earthworms depending on the substrate used in the vermireactor. The results indicate that E. fetida effectively processed the waste materials. Vermicomposting led to a decrease in pH and a reduction in salinity, indicating the progressive stabilization of organic matter. Compared to the initial material, the resulting vermicomposts were characterized by higher nitrogen, potassium, and magnesium content. The content of the analyzed trace elements in the vermicomposts was low, suggesting their potential use as fertilizer. The most favorable conditions for growth of the E. fetida population were observed in the treatment with cellulose (FDMC) added to the structural materials. The results indicate that fallow deer manure can serve as a useful substrate for vermicomposting, especially when combined with carbon-rich structural components.