An advisory committee had recommended either former Seattle Mayor Charles Royer or Triplett. Ron Sims resigned to take a job with the Obama administration. Triplett has spent 17 years in leadership, policy development and management roles in King County government, in the executive branch and on the legislative side. He has served as Deputy Director of King County's Department of Natural Resources and Parks, Senior Legislative Assistant to King County Councilwoman Cynthia Sullivan, and was a legislative aide to State Representative Judy Roland.
Triplett will remain in the executive's post until after the November election.
Six candidates are running in the August primary: County Councilmembers Dow Constantine and Larry Phillips, former KIRO-TV news anchor Susan Hutchison, state Rep. Ross Hunter, state Sen. Fred Jarrett and former consultant and project manager Alan Lobdell.