The purpose of the study was to extract protein from organic grass-clover in a green biorefining process and perform a dose-response feeding experiment with pigs on feed utilization, performance and slaughter quality. Forty-eight pigs were fed one of four experimental diets from 1 week post-weaning to slaughter. The diets consisted of a control diet and diets with 5, 10, or 15 % freeze-dried extracted grass-clover protein included. The extracted protein had a crude protein content of 458 g/kg dry matter, a content of total sulphur-containing amino acids comparable to soybean press cake but a lower lysine content. Acid-insoluble residue constituted 215 g/kg dry matter, and the dominating fatty acid was α-linoleic acid. Addition of grass-clover protein extract to the diet did not affect feed intake or growth in starter, grower, or finisher pigs, and no difference was found in animal slaughter weight. The meat percentage measured at slaughter increased linearly with inclusion of grass-clover protein in the feed. Increased addition of grass-clover increased the content of n-3 fatty acids and lowered the n-6/n-3 ratio in adipose tissue, liver, and Longissimus dorsi muscle as well as the α-tocopherol content. In conclusion, this study shows that protein extracted from organic forages through green biorefining can be used as a protein source for organic slaughter pigs.