In the present investigation, gold NPs (Au-NPs) were synthesized via seed decoction of Nigella sativa, in which, the aqueous seed extract of Nigella sativa acted as a reducing agent as well as coated on Au-NPs surface. Herein, an attempt was made to develop a rapid and biocompatible method to synthesize gold NPs by phytofabrication for anti-diabetic applications. The Nigella sativa seed extract and the Au-NPs synthesized using Nigella sativa exhibited a good antioxidant property, which was determined by the 2, 2-Diphenylpicrylhydrazyl (DPPH) scavenging activity assay. These Au-NPs exhibited 78 \% of anti-diabetic property, which was confirmed by alpha-amylase method. The synthesized nanoparticle Au-NPs size was confirmed by using SEM and TEM. The functional groups (thymoqninone) present in the seed extract as well as Au-NPs were analysed by FTIR. The major functional group i.e. thymoquinone was confirmed by the anthraquinone test and it is responsible for the antioxidant, anti-diabetic, and anticancer properties of the Au-NPs. The phytochemical based nanoparticle prepared in this work showed efficient anti-diabetic activities and it can be considered for the medical applications. In addition, phytochemical based nanoparticle synthesis is safe, eco-friendly, biocompatible, and cost effective.