Labour's defeated Assembly candidate in last month's Blaenau Gwent by-election stood down from next year's election today.
John Hopkins, who lost to independent AM Trish Law by more than 4,000 votes on June 29, said it was time to let someone else have a go.
Labour lost rock-solid Blaenau Gwent at the last general election when AM Peter Law - Mrs Law's late husband - defected in protest against an imposed all-women shortlist.
The unprecedented double by-election prompted by his death saw Mrs Law and her parliamentary running mate Dai Davies keep Labour at bay.
The tough task of regaining the seat is a key plank of Rhodri Morgan's tactic for staying in power beyond 2007.
Mr Hopkins, the leader of the local council, said: "I enjoyed the by-election campaign, despite not being elected.
"I do feel however that now I have fought the by-election campaign it is up to someone else to have a go.
"But there is important work to do for Blaenau Gwent and I fully intend carrying on as council leader.
"I will work my socks off in partnership with our Labour Assembly Government to deliver the rail link on time for summer 2007."
Assembly Finance Minister Sue Essex, who plans to stand down next year, said: "We are all extremely proud of the job John did as the Labour Assembly candidate in the by-election.
"Labour did significantly close the gap on the independents and that was in large part due to the enthusiasm and vision of John."