Deep eutectic solvents (DES) based on choline chloride and hydrogen bond donors are shown to be efficient functional additives for thermoplastic starch, able to act as efficient plasticizers, water uptake inhibitors, and as compatibilizers in the case of blends with a hydrophobic phase. One of the DES tested also prevents the recrystallization of starch. Although such properties can also be obtained with an imidazolium chloride ionic liquid, DES present the advantage of being environmentally friendly and potentially cheaper. Their wide potential in terms of formulation, by adjusting the nature and content of the hydrogen bond donor, opens new perspectives for the development of efficient starch based biodegradable plastics and composites.