An accelerator composition for epoxy resin formulations, the accelerator composition including (i) at least one transition metal complex and (ii) at least one salt where the cation of the salt is a metal or an onium cation with a non-nucleophilic anion; and a curable epoxy resin composition including (A) at least one epoxy thermosetting resin, (B) at least one curing agent, and (C) the above accelerator; a curable epoxy resin composition containing the above accelerator; and a cured thermoset produced from the above curable epoxy resin composition.