Herbal medicine is an imperative portion of both traditional and modern medicines. Medicinal plants have been used in healthcare since time immemorial. This study evaluated the phytochemical constituents and allelopathic potentiality as well as the anticancer activity of Datura innoxia Mill. Plant extracts were prepared to carry out a phytochemical screening. D. innoxia contains alkaloids, flavonoids, phenolics, terpenoids, saponins and amino acids which are mainly responsible for the biochemical and pharmacological activity resulting in high antioxidant activity of the plant. Germination and growth bioassays were conducted on two important crops (Vicia faba and Triticum aestivum) as recipient species. D. innoxia exhibited a strong allelopathic potential suppressing the initial growth and several growth parameters of the two recipient plants. The study inspected cytotoxic effects using four carcinoma cell lines. Plant ethanolic extract showed high anticancer activity especially against MCF-7. This study demonstrated that D. innoxia has high antioxidant activity, valuable potentiality as an anticancer agent as well as herbicidal activity against harmful weeds.