Keir Mather, Steve Tuckwell and Sarah Dyke will take their seats on the green benches after winning contests triggered by the departure of three Conservative MPs including former prime minister Boris Johnson.
At 25, Labour newcomer Mr Mather will become the youngest MP in the Commons – the Baby of the House – after overturning a 20,137 Conservative majority to win the North Yorkshire seat of Selby and Ainsty for Labour.
Shadow education secretary Bridget Phillipson welcomed the Oxford University graduate, who most recently worked for the CBI, saying: “I’m delighted that Keir will be joining us in Parliament, making the case for the people of Selby and Ainsty – we’ve got other by-elections coming up in the weeks to come and that will again be an opportunity for Labour to fight hard for every vote.”
Mr Tuckwell, who held the seat of Uxbridge and South Ruislip for the Tories after the dramatic resignation of former prime minister Boris Johnson, is a former councillor with strong roots in the community.
He said he was “privileged and humbled” to be elected in the place “where I’ve spent all 54 years of my existence” after a campaign which sought to paint the vote as a referendum on the ultra-low emission zone (Ulez).
Ms Dyke, a Liberal Democrat, also has a background in local politics and comes from a farming family in Somerset.
The newcomer, who takes over from former Tory MP David Warburton following his resignation after he admitted cocaine use, said: “I promise to be a different kind of local politician, who will fight for better NHS services, a fair deal for our farmers and more help with the cost-of-living crisis.”
The three arrivals come at the start of a busy period in politics, with party conference season weeks away, the King’s Speech and two further electoral battles imminent.
Labour and the Lib Dems are both vying to flip a 24,664-strong majority in the Mid Bedfordshire seat of former culture secretary and Johnson ally Nadine Dorries.
Meanwhile, a fight for the constituency of Rutherglen and Hamilton, triggered by former SNP MP Margaret Ferrier’s Covid-19 rule-breaking, will be closely fought by Labour and the SNP.
Concerns have arisen that Mr Sunak might postpone the Mid Bedfordshire by-election to avoid scheduling conflicts with the Conservative Party conference, but the Lib Dems plan to table a motion this week for the contest to be held at the start of October.