This study aimed to develop potentially synbiotic yellow mombin (Spondias mombin L.) beverages added with fructooligosaccharides and Lactiplantibacillus plantarum NRRL B-4496. Six formulations of yellow mombin beverages were prepared to measure the influence of fermentation and pH, which was adjustment to 4.5 for stability and quality parameters. Formulations were evaluated for probiotic survival, pH, titratable acidity, total phenolic compounds (TPC), and antioxidant activity for 28 days at 4 °C. Additionally, the proximate composition, color, sensory aspects, and survival to simulated gastrointestinal conditions were studied. At 21 days of storage, the viability of L. plantarum was 9 CFU/mL for the fermented symbiotic (SYNf) and non-fermented symbiotic with adjusted pH (SYNa) formulations. In addition, the fermented synbiotic with an adjusted pH beverage (SYNfA) showed a count of 8.2 log CFU/mL at 28 days. The formulations showed a high TPC (234–431 mg GAE/L), antioxidant activity (48–75 µM trolox), and a potential use as low-calorie beverages. The SYNf formulation showed an acceptability index higher than 70% and a high purchase intent. The SYNf and SYNa formulations maintained suitable probiotic counts after exposure to the simulated gastrointestinal digestion. Therefore, it was possible to develop a new potentially synbiotic yellow mombin beverage with a high sensory acceptance, supplying the market with a new functional food alternative.