Tony Blair will on Wednesday endorse one of his oldest political allies to replace him in the safe Labour seat of Sedgefield.
Phil Wilson - who talent-spotted the former Prime Minister when he was looking for a constituency in 1983 - was installed as the party's candidate on Tuesday night after a vote by local activists.
Now boss of a PR firm, Mr Wilson worked for Mr Blair in Sedgefield from 1987 to 1994.
A by-election has been called for July 19 after Mr Blair quit Parliament to take up a new role as a peace envoy in the Middle East.
The ex-Premier held the seat for 24 years, and had a majority of 18,457 at the last general election.
Hundreds of local Labour party members selected from a short-list of candidates at a meeting held in Trimdon Labour Club.
A Labour party spokesman said Mr Wilson had won by a "comfortable margin".
After the count the candidate said: "I am honoured and overwhelmed by the support shown to me by the members."
The constituency stretches from the outskirts of Durham City in the north and surrounds the town of Darlington on three sides in the south.
