There is a global need to explore alternative protein sources and develop new health-promoting plant-based products. This study aimed to produce beverages from organic seeds of chickpeas and green or red lentils and assess the potential of using L. plantarum 299v to ferment these beverages. Spectrophotometric methods were used to evaluate the ability of the beverages to neutralize 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH•) and chelate Fe2+. Total dietary fiber (including soluble and insoluble fractions) and the protein profiles were compared among the tested legume-derived beverages. The observations were focused on reductions in pH levels, total extract content, dietary fiber, ash, and moisture levels in all the fermented legume products. Fermentation contributed to increased antioxidative activity in all the tested products. The strongest ability to chelate Fe2+ (58.33 ± 2.35%) was noted in non-fermented green lentil products, while green lentil beverages fermented for 72 h exhibited the highest value of free radical scavenging activity (88.44 ± 4.24 DPPH• inhibition %). Chickpea products fermented for 72 h displayed the highest count of viable bacterial cells at 7.0 ± 0.7 × 108 CFU/g, while those fermented for 48 h exhibited the greatest number (2764) of potential biopeptide sequences. These findings highlight the feasibility of using this probiotic strain to enhance the functional properties of legume-based beverages.