Nadine Dorries has announced she will quit as the MP for Mid Bedfordshire with immediate effect.
The ex-Culture Secretary said: "I have today informed the Chief Whip that I am standing down as the MP for Mid Bedfordshire, with immediate effect.
"It has been an honour to serve as the MP for such a wonderful constituency but it is now time for someone younger to take the reins."
The 66-year-old, who was a loyal ally to ex-Prime Minister Boris Johnson, previously announced she would not contest her Mid Bedfordshire seat at the next election.
Mid Bedfordshire's by-election will be Rishi Sunak's first defensive test since entering Number 10
GB NewsDorries' decision comes just hours after the former Culture Secretary claimed she did not want to cause a by-election.
It had been reported that the outgoing Mid Bedfordshire MP had been dropped from Boris Johnson's resignation honours list to avoid a bruising by-election.
However, Dorries' immediate resignation ensures that Prime Minister Rishi Sunak will face a by-election challenge in her safe Conservative seat.
The Brexit-backing author was returned to the House of Commons for a fifth successive election in 2019 with a majority of 24,664.
Nadine Dorries is a fervent supporter of ex-Prime Minister Boris Johnson
PALabour finished in a distant second with 14,028 votes and the Liberal Democrats languished behind in third on 8,171.
But Sir Ed Davey's party will hope to pull off yet another by-election victory in a traditional Tory heartland seat.
The Liberal Democrats would need a 23.6 per cent swing to win Mid Bedfordshire.
The party won Chesham & Amersham in June 2021 with a swing of 25.2 per cent.
The Liberal Democrats see Mid Bedfordshire as Blue Wall territory
PAThe Liberal Democrats snatched North Shropshire after ex-Northern Ireland Secretary Owen Paterson was forced to quit following a 34.2 per cent swing.
Former British Army Major Richard Foord also won the rural Devon seat of Tiverton & Honiton with a 29.9 per cent swing last May.
Responding to Dorries' resignation, a Liberal Democrat spokesperson said: "This is a rural seat in the heart of the Blue Wall, we are in it to win it."
The upcoming by-election in Mid Bedfordshire will be the first time Sunak is forced to defend a Conservative constituency since he entered Downing Street last autumn.
Prime Minister Boris Johnson in front of a giant inflatable of himself as he meets and newly elected MP Jill Mortimer at Jacksons Wharf in Hartlepool
PA
The Tory Party has only managed to pull off three by-election victories since the last general election.
Johnson led the Conservative Party to gain Hartlepool in May 2021 and he successfully defended Old Bexley & Sidcup and Southend West later in his premiership.
However, incumbent Governments tend to perform particularly poorly in both by-elections and local elections.
Alongside three Blue Wall defeats, the Conservative Party lost Red Wall Wakefield to Labour's Simon Lightwood last June and also suffered more than 2,000 net losses in the past two local elections.
