Background: Gastrointestinal (GI) microbiome is a highly diverse and intricate symbiotic ecosystem that offers a multitude of metabolic and adaptive benefits to the host. Diverse phytochemicals consumed as vegetarian diet or taken as food supplements are metabolized intensely in the GI tract and provide a range of nutritional and dietary therapeutic benefits. Insights into the gut microbial-biotransformation and plant-based therapeutics with reference to the diet and their interaction with the host offers development of futuristic dietary therapeutics that could boost the efficacy of nutraceuticals and plant-based formulations for human health. Scope and approach: This review provides insights into the gut microbial biotransformation of selective predominant dietary phytochemicals and the biological activities of the produced metabolites. It emphasizes the potential of GI microbes as probiotics or microbial food additives to improve utilization of plant-based diets, and enhance the bioavailability and bioactivities of phytochemicals. Key findings and conclusions: Vital and pro-health activities of plant metabolites produced as a result of gut microbial biotransformation emphasize the use of gut microbiota as novel probiotic candidates. The inferences summed up in the report could pave the way to develop potential probiotics to increase the efficiency of plant-based therapeutics towards enabling human hosts to cope with metabolic, inflammatory, proliferative, infectious and non-infectious diseases. We believe that the obtained and acquired new knowledge as discussed here has implications to develop dietary therapeutics that could steer the functioning of gut microbiota towards boosting host's nutritional and immunomodulatory efficiency.