Interest in white lupine has increased in recent years in animal nutrition due to its balanced protein and lipid content, phytochemical compounds, and low alkaloid content. Agronomic traits, nutrients, and antioxidant phenols of six white lupin genotypes grown in a Mediterranean area were explored. Genotypes significantly differed in growth stages and life cycle length (from 172 to 204 days after sowing), plant height (from 36.1 to 97.2 cm), seed yield (from 1.02 to 3.50 Mg ha−1), and yield components. Seed yield was positively correlated with the number of seeds per pod and the thousand-seed weight. Across the average of genotypes, a high protein content (397 g kg−1), a low fiber content (133 g kg−1), and oil content (116 g kg−1) with a high oleic acid (453–509 g kg−1) and low erucic acid content (8–17 g kg−1) were found. The n3/n6 ratio varied from 1:1 to 1:4. Ecotype G showed the highest TPC, DPPH•, and ABTS•+ and Multitalia showed the highest content of Apigenin 1 and 2 derivatives. The lowest alkaloid content was recorded in Volos, Luxor, and Lublanc. Overall, this species can be considered a suitable feed crop and a valuable ingredient in animal nutrition due to its overall nutritional profile. At present, only Volos, Luxor, and Lublanc can be suggested in animal nutrition due to the low alkaloid content. Nonetheless, interesting agronomic and quality traits in Multitalia and the two ecotypes suggest room for breeding to reduce their antinutritional factors.