Oilseed press-cakes, a by-product of the oil industry, are currently utilized primarily as animal feed. However, their high protein content and nutritional value make them a promising and sustainable alternative protein source for human nutrition. Their utilization aligns with the principles of circular economy and resource upcycling, promoting a more efficient use of agroindustrial by-products in the food sector. This research featured industrial dehulled sunflower press-cake with the protein content of 44.4% and the total phenolic content of 33.8 mg GAE/g total solids. The functional properties of the micronized press-cake and its protein extract were investigated, with a focus on the impact of ultrasound treatment. Sonication notably enhanced the water-holding capacity by 25% and the oil-holding capacity by 48% in the micronized presscake improving its suitability for applications that require moisture and lipid retention, such as baked goods and snacks. In the extracted protein fraction (72.6% protein), the ultrasound treatment improved the emulsifying capacity by 8.5% and the emulsifying stability by 17%, reinforcing its potential for protein-fortified beverages, sauces, and other emulsified foods. In this research, sonication emerged as a promising processing step worthy of further optimization, given its ability to enhance key functional properties of sunflower materials. Targeted micronization, protein extraction, and sonication made it possible to upcycle sunflower press-cake as a nutritionally valuable and sustainable ingredient in the food industry, either in its micronized form or as a concentrated protein extract.