Labour gained two more MPs overnight with the party's second-highest-ever by-election swing, and a win in an 82-year Tory held seat.
The public hit the polls in Mid Bedfordshire, where Nadine Dorries was MP and in Tamworth, the former seat of Chris Pincher.
Dorries' long drawn out resignation came in anger after ally Boris Johnson didn't award her a peerage in his resignation honours list.
Her replacement MP, Labour's Alistair Strathern, overturned a majority of 24,664, believed to be the biggest since the 1945.
Conservative candidate Festus Akinbusoye saw his party's vote share nearly halved to 31.1%, while the Lib Dems near-doubled their vote share to 23.1% in a seat they believed they had a chance to win, though still finished third.
Double blow for Sunak
Tamworth has been a safe Conservative seat for nearly a century, but last night's results suggests there's no such thing for the Tories ahead of the next election.
The 23.9% swing to Labour shows worrying signs for the party, is history is to be repeated.
Prior to the Labour's landslide win in the 1997 general election, the Conservatives lost four seats to Labour in three years, each with swings of more than 20%. They've now lost three seats in as many months to Starmer's party with swings of more than 20%, suggesting that the next general election could be even more of a landslide.
"For the first time since 1996 Labour’s campaign feels like a juggernaut," posted former Scottish Labour leader Jim Murphy on social media.
Following the historic win, an elated Sir Keir Starmer said: "This is a phenomenal result that shows Labour is back in the service of working people and redrawing the political map.
"To those who have given us their trust, and those considering doing so, Labour will spend every day acting in your interests and focused on your priorities. Labour will give Britain its future back."