The Labour Party has chosen a former Labour aide as its candidate for the by-election in Tony Blair's old seat.
Two by-elections are being held on the same day
Phil Wilson, who runs a public relations company, was chosen by local activists at the Trimdon Labour Club to contest the Sedgefield seat on 19 July.
The Liberal Democrats chose councillor Greg Stone to fight the seat.
The Tories and UK Independence Party have already chosen their candidates for the contest, which follows Mr Blair's decision to quit as an MP.
After the count on Tuesday, Mr Wilson said : "I am honoured and overwhelmed by the support shown to me by the members."
Lib Dem Mr Stone, 32, is a councillor on Newcastle City Council who works as a regeneration expert - including on eco-friendly projects locally.
Lib Dem chief executive Chris Rennard said they would be "challenging Labour hard" in Sedgefield.
He added: "Many people will now want a full time dedicated local MP and Greg will be that person."
The Conservative Party has chosen Graham Robb as its candidate, and the UK Independence Party has picked Toby Horton, a former Conservative candidate who stood against Mr Blair in 1983.
Meanwhile, UKIP has chosen GP Kunnathur Rajan to contest the Ealing Southall by-election, also on 19 July.
He said: "I shall be fighting my campaign on policies which will improve the lives for people in this constituency, including an end to mass uncontrolled immigration, strong policies on law and order and for a referendum on the new proposed EU treaty."
The Lib Dems in Ealing Southall have chosen business manager Nigel Bakhai and the Tories have opted for businessman Tony Lit.
The by-election was triggered by the death of Britain's oldest MP, Piara Khabra, who was 82.