In recent years, 3D printing has become a rapidly developing manufacturing technology with huge potential and is influencing many industries, such as engineering, art, education, medicine, aerospace, and many more. Of the many technologies, the one used most frequently is the FDM (fused deposition modeling) method, which is widely available, relatively simple and inexpensive. The essence of this method is to extrude a thermoplastic material through a heated nozzle in a controlled manner. PLA, or polylactide, is a naturally sourced material with good biodegradable properties. It is frequently used in 3D printing and is derived from natural ingredients such as maize starch or sugar cane. The current study aimed to determine the effects of adding plant-origin food industry by-products, such as carrot pomace and ground walnut shells, to PLA on the mechanical and biodegradable properties of specimens printed using the FDM technology. The assumed research objective is consistent with the issue of sustainable development in the management of by-products from the food industry. The study used a pulverized fraction of each additive, with a particle size of less than 0.2 mm, which was introduced into the base material PLA at rates of 1%, 3% and 5%. The mixtures prepared in this manner were used to print (using FDM technology) standardized specimens, which were assessed for strength (bending and breaking tests) and biodegradability (weight loss after 60 and 120 days of storage under varying climatic conditions). It was observed that the additive increased the bending strength parameters (by a maximum of 44.9%, as compared to the raw material with no additives) while decreasing the breaking stress (by a maximum of approximately 15%, as compared to the raw material with no additives). Using plant additives increased biodegradability (up to 7.6%) compared to the control material.