A biomimetic method of gold nanoparticle (AuNP) synthesis is presented which utilizes a terrestrial weed guduchi (Tinospora cordifolia), as the main bioagent. The method enables rapid synthesis of AuNPs at ambient temperature and pressure, with frugal energy use and no harmful emissions. It is possible to control the shape and size of the product by controlling the metal−bioagent stoichiometry. The electron micrographs of the synthesized AuNPs reveal the presence of particles of either monodispersed spherical or polydispersed triangular, pentagonal, and hexagonal shapes in sizes of 16-30 nm and 25-75 nm respectively. The presence of gold atoms was confirmed from the EDAX and X-ray diffraction studies. FT-IR spectral study indicated that the alkaloids in the plant extract could have been responsible for the reduction−cum−stabilization of the gold ions into AuNPs.