Absorptions commencing at 602.6 nm are detected following deposition of mass-selected C7H4+ in a 6 K neon matrix produced from a 1 : 1 mixture of diacetylene and propyne in an ion source. The 602.6 nm system, and a weaker one near 421.1 nm, are assigned to the A 2E ← X 2E and B 2E ← X 2E electronic transitions of methyltriacetylene cation (C3V symmetry), based on mass-selection, spectroscopic analysis of the vibrational structure, and the excitation energies calculated with CASPT2. Structured fluorescence is detected in the 600–760 nm range upon laser excitation at wavelengths of the CH3C6H+ absorptions. The vibrational bands observed in the absorption and fluorescence spectra are assigned with the aid of calculated frequencies of the totally symmetric (a1) vibrations of methyltriacetylene cation.