A fluorescence lifetime-based methanol sensor was developed, utilizing a solvatochromic fluorescence dye, tris(4,4′-dicarboxy-2,2′-bipyridine)ruthenium(II) hexafluorophosphate. The indicator dye was dissolved in a poly(methyl methacrylate) solution, which formed a thin sensing film for methanol when cast and dried on a glass slide. When the film was removed from methanol-free octane and placed in methanol-containing octane, the fluorophore displayed a lifetime change which was measured in the frequency domain using phase-modulation fluorimetry. At 84 kHz, an 8.8° decrease in phase angle and a 9% increase in modulation were found on substitution of octane with a solution of 2% methanol in octane. The response time for a 95% total signal change was about 22 s. The use of the sensor for gas-phase measurements was also demonstrated. As a blue LED was used as the excitation light source, the sensing methodology can be performed with simple and moderately priced instrumentation.