Nanotechnology, by providing new techniques for creating nanoparticles (NPs) with sizes ranging from 1 to 100 nm, has transformed several scientific and technological domains. The use of hazardous chemicals in conventional noble metal processing has led to a move towards more ecologically friendly alternatives. Because green synthesis is safe, affordable, and scalable—especially when employing plant extracts—it has become a viable substitute. The current advancements in the plant-based green synthesis of nanoparticles (NPs) are examined in this review, with particular attention paid to production methodologies, characterisation methods employing spectroscopy and microscopy, and a range of applications including environmental remediation, food science, cosmetics, agriculture, and nanomedicine. Along with possible biological activities and toxicity considerations of plant-derived NPs, the synthesis mechanisms are examined, including the functions of phytochemicals as stabilising and reducing agents. Utilising plant extracts to synthesise NP offers numerous benefits; one of these is that simple, environmentally friendly methods can be used to customise NP characteristics including size, shape, and content. The size and structure of synthesised NPs must be confirmed using characterisation methods like UV–visible spectroscopy, TEM, and FTIR in order to guarantee reproducibility and their sector-wide application. Applications of plant-derived nanoparticles (NPs) in agriculture show their effectiveness in crop protection and nutrient delivery systems, while applications in nanomedicine emphasise their promise in targeted medication delivery, antioxidant characteristics, and antibacterial activity. The necessity for ethical and environmentally conscious breakthroughs in nanotechnology is further highlighted by the need for improved research into the environmental effects and biocompatibility of these nanoparticles.