Lactic acid bacteria (LAB) have been used for centuries to produce fermented foods. Cruciferous vegetables contain large amounts of health-promoting compounds such as glucosinolates (GLSs) and phenolics. GLSs and phenolics have been linked to antioxidant, anticancer, and immunosuppressive effects. However, it has been reported that some LAB strains are able to metabolize and enhance the activities and amounts of biomolecules through decarboxylation and/or reduction activities, with positive impacts on human diet and colorectal cancer (CRC) prevention. In the present work, the bioprocessing of broccoli by lactic fermentation was evaluated to produce a functional food using both spontaneous and induced fermentation (Levilactobacillus brevis and Lactococcus lactis as starter co-culture). Changes in the proximal composition, GLSs, and phenolic content as well as the antioxidant, antiproliferative, and immunosuppressive effect of the fermented product were evaluated in in vitro cellular models to validate their potential in CRC chemoprevention. The results demonstrated that fermented broccoli extracts increased the antioxidant activity in Caco2 cells and inhibited the proliferation of HT29 and HT116 cell lines in a concentration-dependent manner, with the best results on day 6 at a concentration of 600 µg/mL. Our findings also provide evidence that fermented broccoli could have an anti-inflammatory effect.