A novel di-silylated fluorescein probe, bearing two triethylsilyl-protected phenolic oxygens, was synthesized via a direct, metal-free functionalization of fluorescein and evaluated as a dual-responsive turn-on fluorescence sensor for the discriminative detection of fluoride (F⁻) and hydroxide (OH⁻) ions. In its native state, Probe exists predominantly as a non-fluorescent, closed spirolactone; exposure to F⁻ or OH⁻ triggers Si–O bond cleavage, restoring the fully conjugated fluorescein chromophore and producing a marked colorimetric (colorless-to-green) and fluorogenic turn-on response. The two analytes are resolved through two mechanistically distinct pathways: F⁻ reacts via direct, nucleophile-specific attack at silicon, dominant in the aprotic solvent CH₃CN, while OH⁻ reacts via a base-catalyzed pathway compatible with the protic solvent EtOH allowing solvent- and kinetics-based discrimination of the two ions from a single probe. Probe displayed high sensitivity and a wide linear response range for both analytes, with detection limits as low as 29.25 nmol/L (F⁻) and 12.32 nmol/L (OH⁻) by fluorescence and showed no response toward non-basic spectator anions (Cl⁻, Br⁻, I⁻, SO₄²⁻, NO₂⁻, NO₃⁻). The practical utility of this discrimination strategy was demonstrated in spiked DI water samples, where F⁻ and OH⁻ were accurately quantified both individually (99.9–103.6% recovery) and as a mixture, using a kinetic subtraction method to resolve both analytes from a single sample (104.0–104.2% recovery). This work establishes a dual-channel sensing platform for fluoride and hydroxide detection in aqueous systems, with potential application in water-quality monitoring.