An unsaturated quaternary ammonium salt is produced by a process that includes reacting methyl chloride in a first vessel with a stoichiometric excess of an unsaturated tertiary amine in the presence of water to form a reaction mixture that includes the unsaturated quaternary ammonium salt and residual unsaturated tertiary amine. The reaction mixture is transferred to a second vessel and phase separated to yield a first fraction in which the unsaturated quaternary ammonium salt is concentrated, and a second fraction in which the residual unsaturated tertiary amine is concentrated. At least a portion of the second fraction is recycled from the second vessel to the first vessel for use in the reaction with methyl chloride. The process, which is preferably operated continuously, allows the use of reduced reaction pressures compared to processes utilizing a stoichiometric excess of methyl chloride, and it also reduces or eliminates the problems associated with recycling methyl chloride and removing methyl chloride from the unsaturated quaternary ammonium salt product.