<p>The unsustainable use of chemical fertilizers has resulted in soil degradation, nutrient imbalance, and environmental pollution, driving the urgent need for renewable and eco-friendly alternatives. Seaweed biomass, a widely available marine resource, has emerged as a promising feedstock for the development of organic fertilizers due to its rich composition of macronutrients, micronutrients, and bioactive compounds. This review critically examines the potential of seaweed-based fertilizers, positioning them as a unique category of biofertilizers that go beyond traditional organic inputs by acting as both nutrient sources and plant biostimulants. The paper consolidates findings on nutrient composition, biochemical pathways, and nutrient release mechanisms, highlighting how seaweed fertilizers improve soil fertility, microbial activity, and water retention while reducing dependency on synthetic fertilizers. Special attention is given to comparative insights with conventional organic amendments, such as animal manures and compost, to demonstrate their superior efficiency in enhancing crop yield and resilience to abiotic stress. The review also explores innovative approaches, including nano-seaweed formulations and integration into aquaculture–agriculture systems, which enhance nutrient availability, uptake efficiency, and overall sustainability. By identifying research gaps in large-scale production, biochemical interactions, and long-term soil health impacts, this study provides a critical perspective for advancing commercialization and policy frameworks in seaweed-based fertilizer development. Ultimately, the paper underscores seaweed fertilizers as a viable strategy to reduce environmental footprints, restore soil health, and support sustainable food systems in alignment with global climate-smart agriculture goals.</p>