The influence of pressure on structural, electronic, and optical properties of choline iodide is studied within the density functional theory approach using the РВЕ gradient functional, the D3(BJ) dispersion correction, and a basis set of localized orbitals. Elastic constants, parameters of the Birch–Murnaghan equation of state, density of electronic states, and frequencies of normal longwave vibrations are calculated. It is shown that the immediate environment of the iodine atom contains 12 carbon atoms with the shortest O–H⋯I distance equal to 2.486 A. The О–H distance increases slightly together with pressure, and the I–H distance decreases while its linear modulus is an order of magnitude smaller than the bulk modulus under 97 GPa. In contrast to intramolecular vibrations, the pressure shifts of lattice vibrations exceed 10 cm–1/GPa, and their modal Gruneisen parameters are an order of magnitude larger.