Much attention has been recently paid to the design of sustainable processes for the production of functional food additives based on renewable resources. Thus, methods for incorporation of green techniques in treatment of undeveloped biomass, resulting in value-added bioproducts, are in great demand. We focus here on the biological activity and chemical properties of Erigeron canadensis (horseweed) functional food fiber, which can be strongly affected by the extraction procedure employed. In the present contribution, we report on an attempt to introduce a sustainable and energy-efficient ultrasound-assisted extraction process, followed by a multistep purification procedure, resulting in a macromolecular plant-derived anticoagulant agent. The most efficient ultrasound-assisted process was determined by optimization through the response surface methodology I-optimal design (2⁴). A comparison with the conventional procedure for retrieval of horseweed biomacromolecules revealed that the optimized ultrasound-assisted extraction was more sustainable, with the cumulative energy demand being 38% lower (12.2 MJ), 6.6 times reduced water consumption (3.5 L), and 1.2 times shorter (41 h) total processing time. Moreover, the optimal ultrasound-assisted extraction process-purified food fiber turned out to be a better anticoagulant agent by 57%, compared to a conventional product, and was a more selective indirect inhibitor of the human Xa coagulation factor.