A method of preparing a pre-formed elastomer/filler composite of a diene-based elastomer and particulate filler dispersed therein by polymerizing monomers in the presence of said filler with a polymerization promoting catalyst in which at least a portion of said catalyst is pre-deposited on said filler. Such pre-formed elastomer composite is also contemplated as well as a rubber composition comprised of a blend of such pre-formed composite and at least one additional elastomer. Such filler may be, for example, precipitated silica, carbon black and/or a modified carbon black. A tire having a component of such composite or rubber composition such as, for example a tread, is also provided.