It is shown how to assemble three particles into a single “colloidal trimer”. The particles may consist of different materials and be different sizes, and they can be assembled in a particular sequence (i.e. 1-2-3 or 2-1-3 or 2-3-1). Several trimer assemblies are demonstrated, including polystyrene–silica–polystyrene, gold–polystyrene–silver, and gold–silicon–silver. The gold–silicon–silver assembly operates as a catalytic motor, moving rapidly by autoelectrophoresis when placed in a hydrogen peroxide solution. The assemblies are made by allowing oppositely-charged particles to aggregate in a diffusion-limited manner for a time, and then quenching the aggregation by the addition of a nanoparticle coating on one of the particles. We call this method “Quenched Electrostatic Assembly”, and it serves as a general, scalable method for synthesizing multi-component colloidal trimers, including those requiring a certain sequential order, but not requiring particular orientations. In addition, when polymer nanoparticles are used to quench the aggregation, they can be fused above their glass transition temperature to produce assemblies that are mechanically stable.