Over 2 billion people are unable to access safe, nutritious and sufficient food year-round. While global fisheries are considered key in providing essential nutrients to hundreds of millions of people around the globe, the specific contribution of small-scale fisheries to the nutrient supply given other available food supplies is unknown. Here, we combined multiple global databases to quantify the importance of marine small-scale fisheries to national-level nutrient supply of coastal populations. We found that, on average across assessed nutrients (iron, zinc, calcium, DHA + EPA and vitamins A and B12), small-scale fisheries contributed about 32% of overall global seafood nutrient supply, 17% of the nutrient supply from animal-sourced foods and 10% of nutrient supply from all foods. These global averages, however, underrepresent some key roles of ocean-based foods. Combining nutrient supply estimates with global estimates of inadequate nutrient intake, we found that about half of coastal countries that have a mean inadequate intake of at least 50% across assessed nutrients (iron, zinc, calcium, DHA + EPA and vitamins A and B12) rely on small scale fisheries for at least 15% of mean nutrient supply, and many rely on small scale fisheries for more than 30% of mean nutrient supply. Catch from small-scale fisheries is particularly important for the supply of vitamin B12, calcium and DHA + EPA, representing up to 100% of supply in selected countries. Our study demonstrates the significance of small-scale fisheries for nutritionally vulnerable coastal populations, emphasizing how effective fisheries management can contribute to public health.