Trimethylphenylammonium hydroxide is primarily used as a catalyst in organic synthesis, particularly in the production of polyurethane foams. It accelerates the reaction between isocyanates and polyols, ensuring efficient foam formation with desired properties like flexibility and density.

In analytical chemistry, it serves as a phase transfer catalyst, facilitating reactions between compounds in different phases, such as aqueous and organic solvents. This makes it valuable in synthesizing complex organic molecules and in certain polymerization processes.

Additionally, it is employed in the preparation of specialty chemicals, including quaternary ammonium compounds, which are widely used as surfactants, disinfectants, and fabric softeners. Its strong basicity also makes it useful in deprotonation reactions and as a reagent in various chemical transformations.