Modern agriculture faces mounting challenges from climate change, soil degradation, and the overuse of synthetic agrochemicals, which contribute to environmental pollution, biodiversity loss, and the emergence of more resistant pests and diseases. Plant-derived biostimulants have emerged as sustainable tools to improve crop productivity while mitigating ecological impacts. Unlike conventional fertilizers that primarily supply nutrients, biostimulants act through diverse physiological and molecular mechanisms, including phytohormone regulation (e.g., auxin-like activity), activation of antioxidant defenses, and modulation of the soil microbiome. These actions enhance nutrient use efficiency, strengthen tolerance to abiotic stresses such as drought and salinity, and improve crop quality traits. Plant extracts rich in bioactive compounds, such as polyphenols and signaling compounds, have demonstrated strong potential to stimulate root development, increase photosynthetic activity in crops like tomato and wheat, and promote soil health. Despite these benefits, several barriers hinder their large-scale adoption, including the need for standardized extracts, consistent field performance across diverse conditions, and harmonized regulatory frameworks. This review highlights successful applications of plant-based biostimulants in major food crops and explores recent innovations in their production from agri-food by-products, with particular focus on advanced extraction methods (intensified by enzymes, microwaves, and ultrasound) and formulation strategies (such as emulsification). Ultimately, this work underscores the role of plant-derived biostimulants in fostering more sustainable and resilient agricultural systems, aligning with global food security and safety goals.